16 Feb 2013 02 Jun 2016
There are many guides already but I'm only going to give some tips for what I thought were the harder challenges, the par time for those I completed last.
Most of the time it's only a matter of taking the shortest route and few retries, but for the following levels I was still struggling, until I made a change that then made it very easy.
Make sure you try the Time challenges on their own as it's easier then. For health/headshots/accuracy, just do a dedicated pistol run and take it slow and easy.
For the other challenges please read the other solutions. Also play the missions at least once first, as it will make my explanations easier to understand.
Going Deep (Par Time)
The trick is to use sticky bombs, to blow up the trucks and cars before anyone gets out of them. That includes the first ones (those you need to wait the guys from, to get close to your car, in a normal run). So simply hide the bomb and run behind the red car where the marker is, after a couple of seconds run towards the entrance on time to sticky the first two vehicles. Then get the next vehicles the same way. When you have the marker on top of the ramp, ready your RPG, go up to it and shoot the last truck coming on the left. For the last two cars on the right use any gun as it's simple enough and drive back home following the quick route going through the park.
May take you a couple of tries as you will miss some throws at first, but when you get it right it will save a lot of time. I'd recommend auto-aim off for this.
(you could also try all with RPG but space is tight and I was blowing myself up)
Dropping In (Par Time)
The Bullet GT trick is required (calling the car before starting the mission, see other solutions for details), but on top of that, use the explosive shotgun once in the building. I found it kills faster than the pistol or machine guns and will allow you to easily Rambo your way through.
Departure Time (Par Time)
Big change here, basically don't do it the regular way.
The idea is to avoid all fight and throw sticky bombs over walls to blow up drug caches. Once at Funland kill the two guys in front of you then run back towards where you got off the car until you get to the level of the blue square (drug cache) on your right. Throw a bomb over the wall, start running back to entrance of Funland (giving time for the bomb to land) then blow it up. You will now get a marker at the entrance you need to trigger, but also quickly shoot the two ducks there. Then run back again as fast as possible all the way to the street where you got off the car (ignore anyone shooting you) and turn left; at the second zebra crossing you should be at the level of the last drug cache on your left. Bomb over wall/building and you're done. You will be on the other side after the cut-scene.
For the rest: Kill the running man as fast as possible; run to the bike, be fast but patient on it (will feel slow once the chopper appears, just take it easy and stay behind the enemies); use explosive shotgun on plane and parachute all the way to the park/marker after jumping from the plane.
The Funland part especially will save a lot of time, I made it in under 7 min vs 11 min before.
This Ain't Checkers (Par Time)
Small pointer on this one, for the boat part, use the furthest away. I found it fast yet nimble so is the best for what is the longest part of the race.