Firstly, an admission: the following is based on a pretty deep knowledge of the Dreamcast versions of the game. I've played through the PAL, NTSC, and Japanese versions in the last three weeks, getting Jet ranks in *everything* on all three of them, so I reckon I've sussed the game out pretty well.
Having now played through the HD version once, I can confirm that all these strategies still work.
Also: many many MANY thanks to Cackman on YouTube for his comprehensive series of videos! All credit to him for the techniques in those videos (they're videos of an emulated Dreamcast version of the game), though I will point out areas where his ideas and mine differ somewhat.
There's still no level select in the HD version, so you've got to play through the game in order to get to a specific level. There's a "New Game +" feature - you can just load up a save file and keep playing from the beginning of the game, and your best scores persist in the save file (meaning you don't have to get Jet on every level on a single playthrough... but it *does* have to be on the same save file) - but it's still a bit of a pain.
However, if you want to tackle the Jet rankings sequentially without having to play the whole game again if you mess up, there's a couple of familiar techniques you can use:
1. Backup your save(s) to a memory unit prior to starting every level. That way, if you fail to Jet a level, you can copy your previous save back and try again... OR...
2. On the score rank screen, as soon as you see that you've failed to hit Jet rank, QUICKLY hit the Guide button and then X to sign out. This will prevent the game from auto-saving your progress. Then you can log back in and try again.
You can also your progress through the "Stage Scores" menu, accessed via the pinball machine in the Garage.
Onto the Tips!
To obtain this Achievement, you not only need to get Jet in all the story missions, but also the Jet Graffiti, Jet Crush, and Jet Technique levels too.
It's important to realise that the rank is based entirely on score - the higher your score, the higher your rank. So everything you do should be focused on upping your score - that includes tricks and graffiti. In addition, it's worth remembering that you score additional points at the end of a level:
1. Remaining Life x 30
2. Remaining Time x 30
3. Remaining Spray Cans x 100
4. If Remaining Life is 100% = 3000
So you can see that it's *really* important to finish the level with high, if not full, health.
When spraying graffiti, you get more points for complex actions: 100 points for a vertical move, 200 for a half-circle, 400 for a full circle. When you're painting a L or XL tag, the more consecutive tag combos you make, the more complex the combos become - leading to more points. However, the Graffiti skill rating dictates how complex the combos can be; the character skill ratings are as follows:
Low: Tab, Garam, Slate, Love Shockers, Pots
Medium: Beat, Mew, Cube, Combo, Poison Jam, Noise Tanks
High: Gum, Piranha, Yo-Yo, Goji
If you want a high score, *always* use a character with a High graffiti skill ranking: though the graffiti hieroglyphics are much trickier (you'd better get your thumb joints warmed up), the potential for scoring is much higher, as demonstrated below (assuming you don't mess the tag up, which resets the combos back to the beginning):
Low Graffiti Skill XL Tag: 100 + 100 + 200 + 400 + 400 + 600 + 800 = 2600pts
Medium Graffiti Skill XL Tag: 100 + 200 + 400 + 600 + 600 + 800 + 800 = 3500pts
High Graffiti Skill XL Tag: 400 + 600 + 600 + 600 + 600 + 1000 + 1200 = 5000pts
Always try to get all the XL tags without a mistake - messing up on the sixth section of an XL tag will cost you 1000pts overall! (since your score will then be 400 + 600 + 600 + 600 + 600 + 400 + 600).
When it comes to speed, there's only two real tips (apart from learning all the shortcuts through levels). When using your boost, you only get five "white flashes" of speed before having to "recharge"; however, if you jump and release the boost trigger, the recharge will be instantaneous. So get into the habit of boosting for four white flashes, then jumping, and release the boost trigger while in the air. When you land, you can re-engage the boost for more speed. This trick is especially useful in races and Jet Crush mode.
Grinding rails can be quicker than just skating, but you will slow down over time (and there's no grind button like there is in JSRF). However, small jumps can speed you up. Wall riding is also another way to increase momentum. It's important to grind / jump / wall-ride wherever possible because these tricks give you points - and the more tricks you can string together without touching the ground, the more points you will get. (A simple grind starts at about 10 points and will escalate up to 100 points). So keep grinding and jump from rail to rail, wall-riding where necessary.
The Graffiti Levels
The most important thing: *always* use a high graffiti character (Gum if it's your first run through, or Goji if you've unlocked him - he has a much higher can capacity). This is the *only* way you'll be able to get enough points to hit that Jet rank.
Next, figure out a decent route through the levels - Cackman's YouTube videos ( http://www.youtube.com/user/cackman
) are a brilliant start (though his Benten Burning run seems to depend on oodles of luck). They're the videos included below.
Always try to get all the XL tags without a mistake - messing up on the sixth section of an XL tag will cost you 1000pts overall! And, in levels with green (optional) tags, try to hit as many green tags as possible - *especially* the XLs and Ls.
The Boss Levels (or "Tagger's Tag")
Check back at the end-of-level scoring overview... due to the lack of graffiti in these levels, it's important to finish the levels quickly, with most of your health, and with as many cans of paint left as possible. If you've only got a handful of tags left on your final adversary, fill up on paint and health before finishing them off.
Always use a character with a high can capacity - Tab is a good selection early on, Slate later, and Noise Tanks have a massive capacity (if you've already unlocked them). Try to fill up to capacity before you start attacking for the first time - each level has a convenient cluster of paint - then return to top up when you're nearly done.
The paths that the opposition take are pre-determined; if you lose track of them, just head to one of their regular start points (they'll wait there until you catch up to them). Check your map for their positions!
Having said all that... these are all much easier than the graffiti levels; there shouldn't really be many problems here.
Shibuya GG -- Jet target: 33,000
Love Trap -- Jet target: 41,000
The Monster of Kogane -- Jet target: 30,000
No. 540 -- Jet target: 33,000
Kogane Circus -- Jet target: 29,000
The bulk of your paint will be from the rails in the centre of the level. There's some blue cans in the half-pipe loops, but they can be tricky to grab quickly. There's one health can in the room where Poison Jam start, and one on the centre rails.
Benten Boogie -- Jet target: 44,000
It's best to clear the large tags on the ground level after the initial XL (as shown in Cackman's video).
Graffiti High -- Jet target: 32,000
Noise Reduction -- Jet target: 29,000
There's heaps of blue cans on the upper rails at the top of the map, and a lot of health on the road at the top.
Love Attack -- Jet target: 29,000
The side street (the one with the stairs, which also has health) has 15 paint (3 blue), and a rail leading up to the top of the stairs in an adjacent street has another 10 cans. There's a ton of paint on the rails on the two main streets, too. There's a lot of health at the bottom of the level, and paint a-plenty on rails bordering the two main roads.
Tag or Die (Bantam Street) -- Jet target: 40,000
Rock'n Roll Grind -- Jet target: 50,000
This one is really tricky to do on your first playthrough, when you've only got access to Cube and Combo; to have any chance of hitting Jet, you cannot mess up your XL tags at all, you have to finish with full health, and do it all pretty quickly.
Explosion -- Jet target: 70,000
Fight or Flight -- Jet target: 62,000
This is widely regarded as the hardest level to Jet; the important things here are to grab all the green tags you can (especially the XL at the start of the level), and to exploit the jump into the sewer (which respawns you between the Golden Rhinos without alerting them, allowing you to tag the two XLs in peace). Also, when you see the message that Assassin #2 is on his way, you can take time out to hit GREEN tags - the original Golden Rhinos would have disappeared, and Assassin #2 won't show up until you hit the next red tag. Don't go too far out of your way, though - the time limit is pretty tight on this level.
One thing I've noted with this version of the game: the snipers seem to take a little longer to appear than in the Dreamcast version. This is especially noticeable when you get into the sewers - you can perform the exploit jump before the sniper has appeared - but thankfully it doesn't appear to affect the general strategy of these areas much.
Benten Burning -- Jet target: 50,000
Behind The Mask -- Jet target: 30,000
There's 30 cans near the corner with the entrance to the big spiral: 4 blue cans above ground level (grind the rail to get up to the first two, then turn around to see the other two), then another 10 yellow cans on the ground. Health can be found near Poison Jam's starting position as well as under the aforementioned rail.
Here's the (approximate) scores to hit Jet in the Jet Graffiti mode. These are mostly pretty easy - hit all the red tags, getting any green tags you pass on the way, and make sure you hit the green XLs (and most of the Ls). Time shouldn't be a problem.
The only tricky one amongst these levels is Grind Square. Here, you pretty much have to hit *every* tag (especially the two green XL tags on the upper level on the raised-elevator side), and do it fast, finishing with full health and nearly full cans.
Shibuya -- Jet target: 80,000
Benten -- Jet target: 78,000
Kogane -- Jet target: 72,000
Bantam Street -- Jet target: 70,000
Grind Square -- Jet target: 68,000
Here are the times to beat for Jet ranks, along with Cackman's videos. Every Crush has a shortcut or exploit of some kind; his videos show the best moves, though I'd add that wall-riding in Bantam Street can speed things up a bit.
Remember the boost-jump-boost trick to speed up your times!
The fastest characters are Yo-Yo, Love Shockers, and Pots.
Shibuya - Beat: 88s
Benten - Tab: ~84s
Kogane - Gum: 115s
Bantam Street - Combo: ~68s
Grind Square - Cube: 62s
Note that, on the HD version, grinding up the handrail in the building does not appear to work anymore. This makes it *much* harder to successfully Jet; I recommend using Pots, and grinding up the wall halfway, and jumping from the flat section in between floors. This is, by far, the toughest Jet Crush.
These are also pretty easy to Jet; just pick a high Technique character (Mew or Yo-Yo are usually fine) and hit one of the infinite grind loops that Cackman demonstrates in the videos below.
Shibuya -- Jet target: ~45,000
Benten -- Jet target: 50,000
Kogane -- Jet target: 55,000
This is my pick for the easiest spot to do your 100+ trick combo.
Bantam Street -- Jet target: 50,000
Grind Square -- Jet target: 35,000
In summary (or TL;DR ;)
Don't mess up XL tags.
Use a high-graffiti character - Gum or Goji - for the normal levels.
Use a high-capacity character - Tab, Slate, or Noise Tanks - for Tagger's Tag levels.
Jet Graffiti: Use a high-graffiti character, and hit all the L and XL green tags in addition to the reds.
Jet Crush: Use a fast character - Yo-Yo, Pots, or Love Shockers.
Jet Technique: Use a high-technique character - Mew is my favourite :)