A couple of other posted guides gave good advice; however, for those that are new to DOOM or are having trouble with this, I wanted to give a little more detail on how to increase your chances for this achievement.
Choose the I'm Too Young to Die difficulty as difficulty does not matter for this achievement and it is the easiest. You start off with 3 lives and you can collect 11 more lives in the three levels of the DLC (4 in the 1st level, 3 in the second, and 4 in the final). I recommend you pick up all of these
as it will give you more of a cushion to make mistakes. If you get every life, you can die 9 times. I would make sure you have the bulk saved up for the final boss fight. I think I died twice, once on the final boss and once when I got careless during an arena.
Thanks for @FartingDolphin7 for pointing out that no matter what you unlocked in the base game, you start with all unlocks in the DLC.
I'm not 100% sure because I unlocked all possible upgrades on my regular campaign, but the new DLC may start you with what you unlocked previously. Let me know in the comments and I will update the guide, but if you are having trouble and do not have all upgrades unlocked from the base game, I recommend going back and doing that.
Third: While a previous playthrough is not required, I highly recommend it so you can get a feel for the level, spawns, and locations of the extra lives. You could go for some of the collectible related achievements in this run, but I do not recommend it because you have to fight more enemies and increase your chances of losing lives. Try to get the other achievements on a regular playthrough first.
Thanks to @Dave Bodom for pointing out that while the game says it is disabled, you can still use the extra life support rune. A few players have reported that the achievement unlocked for them despite them using it as well.
While the support runes in the DLC are nice, you CAN'T use the support rune for getting your extra life back after death. It can still be helpful to get one of the support runes, but be aware you can't use the extra life one. If you know which one you want,
I recommend getting the support rune in the second level as it is at the beginning and you don't have to do a slayer gate to obtain it.
With the above information, you should be ready to start the game. Here are some general tips I found helpful to keep from losing lives:
-Use belch (flame) frequently.
I always used it going into a battle and would continue to use it, especially on bigger enemies, to refill my armor during the fight. In between belch uses, the meat hook on the super shotgun is a good substitute.
-Make frequent use of your Blood Punch.
If I saw my health was not full and I had 2 built up, I would use one to refill as I was glory killing a lot and it fills up quickly. I would keep 1 in reserve for emergencies/low health situations as it can get you out of a bind
-Plan out BFG ammo.
I use BFG for emergencies, but if you see an ammo in an upcoming area and you're full, be sure to use it in a big battle so you don't waste a potential round by having to pass it up. Usually the hardest enemies spawn near the end of a battle, so once your least favorite enemy shows up, unload.
-Make good use of Auto Aim.
Two of the new enemies can be taken out fairly easy using the precision bolt and auto aim. Simply get your reticle kind of close to the weak area, LT to aim down the sites, and you can fire almost immediately for instant weak spot hit.
-Before going into a battle arena, try to get a handle on where major health pickups/powerups are
. I saved them for when I started getting kind of low and then would make my way towards them while still killing enemies. Some battle arenas start immediately, but others a player action is required to start.
The next few tips contain spoilers:
If you have any recommendations to add to the guide, let me know and I'll add them.