If you played the last Saints Row game, then you should be able to get this done easily. For new players, you need to get deliberately hit by incoming traffic; it's better to get hit multiple times by multiple cars to earn multipliers and increase your score. It will be much easier this time since you have powers. Do a charged jump then control your landing. Press LT or RT to roll upon landing. This may require timing and control but you can repeat this and reap a bucket load of cash.
Tank Mayhem (Easy)
This a really fun activity since you just need to blow things up within the time limit. The tank has two weapons: a continuous-firing laser and its main turret. Keep holding the laser while you move around and firing the turret.
Speed Rift (Medium)
This is part of the side quest “Something to Prove”
This is part of the side quest “Secret Admirer”
This is part of the side quest “Kill Kill Destroy Kill”