Tires,springs,engine,fuel is a good start. Tires- Find out what type of track you will be racing on, hard packed,dirt,clayect and then refer to Prolines web site and check out there tire chocies and recomendations.They will tell you what tire works best in what condition.
Springs-softer for bumby, stiffer for smooth Engine- (This is only my opinion) I like the .15's personaly, but some tracks require you to use a .12. ROAR events requires it.A lot of people like the .12 because of the weight differance, which is not a lot, and they still have a lot of power. Fuel- i like o'donell 20%.