There are 40 long jumps across Palm City, I recommend leaving these until after you hit REP level 50 and have unlocked the Regera. It’s pretty much a case of lining yourself up with the jump the flooring it, use your NOS at the right time to get the greatest speed boost, hit the middle of the jump, sit back and wait for the landing.
You only need to get 1 star across all 40 long Jjmps to unlock your Trophy / Achievement.
However, if you’re going for the Platinum or 100% of your GamerScore, you will need 3 stars across all 40 jumps
Below is a video showing the locations and how to get 3 stars in all 40 long jumps.
As soon as you have at least 1 star in each of the 40 long jumps, your Trophy / Achievement will unlock