1. Drive in the bumper cam mode, the one with the rear view mirror. This allows you to easily see what's going on behind you.
2. Learn your brake points, and understand that if you're drafting somebody, your brake point is now different.
3. Don't follow right behind somebody until you're comfortable with how they drive, and even then - I wouldn't follow directly behind someone until higher DR, lower skill drivers are unpredictable.
4. Just because you are going faster than somebody in front of you, doesn't mean it's a passing opportunity. Especially in the slower cars, trying to go 2 wide through a technical section of course usually will just slow you both down - and at lower DR's most drivers won't know how to give space for another car when they're not used to it.
5. Winning races is just as much about being consistent as it is about being fast.
6. Don't retaliate, if somebody pushes you off track, or slams into your rear end, don't try and "teach them a lesson" - it'll just make things worse.
7. LEARN the tracks - seriously, go to circuit experience and get all gold for the track you're about to race.
8. Watch for brake lights, they're hard to see in this game - but they are there, and are a valuable resource when you're in a pack.
9. If you see what looks like a dangerous situation in front of you, or a wreck happening - don't try and barrel through it at full throttle. Yes sometimes you can hold the gas and get through unscathed, but 9 times out of 10 you won't. You'll have a much easier time navigating trouble/accidents when you simply come off the gas (you don't necessarily have to hit the brakes).
10. Watch the fastest lap replays, and turn on telemetry so you can see their braking / throttle and get an idea for how they drive the track.
11. Drive clean, you won't learn anything from using other peoples cars as barriers, or dive bombing every corner.
12. Just because you don't win, doesn't mean you had a bad race.