I would highly recommend beating the entire storyline before trying to complete any of the activities. The jump ones are pretty easy but some of them still require upgraded cars.
I used the Regera which is the fastest car in the game for the speed traps and speed runs. The traps are the second easiest of all activities to complete three stars. Just line up a pretty good distance from the speed traps and gun it till you hit 3 star speed. The speed runs were by far the hardest ones for me to get. These you just have to stay patient on. Hitting the required speed is not too hard but doing it while dodging all the traffic in the game is frustrating. Nighttime definitely has less cars spawn so if you're stuck on one, move on to another for the time being, and just return to the hardest ones when it gets dark. Your character will usually say something about it being night time and that's when you'll know it's transitioned over. You shouldn't have to upgrade the Regera anymore than stock but I would recommend trying to get full outlaw for extra Nitrous and top speed.
The drift ones are definitely the second hardest. I used an almost fully upgraded BMW M5 because I used it for the 350,000 score achievement also and got used to how it handles. It has good speed, handling, but it is rather bulky. There are only a couple drift locations that are pretty difficult but same as the speed runs, you just need to be patient. You'll be doing pretty bad on some runs and then completely blow it away all of a sudden. I recommend getting some good speed going into the start of these activities or even drift the corner into the starting line so you get a good feel for the road.
For all of the activities except for the jumps, you are able to hit from both sides so take a look at the map to see which direction will work best for you. Most speed traps will be obvious which direction to take, but some can be done from either direction. For the drift activities, some might be easier going uphill and some downhill. I found dirt drifts to be easier going uphill for the most part.
Sorry the guide is a long read but these are some pointers that I have for trying out this achievement. I am currently one drift challenge away from all 3 stars. Hope this helps, feel free to message me for anything you might need.
Update 1:
I used a virtual interactive map to uncover most of the activities found at:
http://swissgameguides.com/maps/need_for_speed_payback/world...
They do not have the drift locations on that map yet though. But if you go for all the collectibles first, you'll uncover a great deal of activities. The only downside is that you practically have to drive through the starting line to discover it on the main map but you will see them on the mini map at all times when you're near them.
I did find a video on YouTube that shows all the activities. Luckily I only needed it for locating one drift activity which was in the city that I hadn't discovered.
https://m.youtube.com/watch?v=RhcIBxZ16N4