I find one of the best things you can do is download some of the fastest hotlap replays, and see what lines they are using, brake and entry points, even listening to throttle changes and watching steering inputs helps you see what it takes to get a car around the track that fast.

I always learn something, and sometimes my apex point was just horrible when comparing it to a WR replay. Braking too late rather than too early will always cost you more time.

As mentioned, a wheel, while not strickly neccesary, is a massive bonus. I'd get something with FFB (I don't have that on mine, but I miss it just the same) if your able. The level of car control you lose out on when you can't feather the throttle and brakes is a lot. Trail braking, using the throttle to turn the car, etc... these are all almost impossible to do with a mouse, but very rewarding when you get them down pat on a wheel setup.

2 cents.