Here are some tips:
-perfect shifts are gotten in a range of ammount of RPM's, if you get in the higher rpm limit, you will finish the race faster. i.e. if you get perfect shift between 6700 and 7000 rpm, try to shift close to 7000 instead of 6700.
-The best nitrous boost is about half a second after third gear to avoid loosing it during the shift process. If you have very good flywheel and gearbox, reduce this time accordingly.
-It doesn´t matter if you win by an inch or a mile, so, if you can sacrifice the nitrous in 3rd gear and use it close to the end, you will take longer to reach the finish line, but your top speed will be higher, giving you a chance for one more perfect shift, which gives you bonus coins.
-Ladder drags consist only of quartermile races, while challenges are 1/4, 1/2, 1/4, 1/2, and 1/2 miles, high acceleration cars are favored in quarter miles, while high top-speed cars are favored in half miles.
-It is not as important to upgrade shifting time on 4-gear cars (regularly the vintage kind) as on the 6-gear cars.
-if you have the gold, get extra fuel slot.
-Spending coins gives you xp, for every 66.67 coins spent, you get 1 xp approximately.
-Play it safe. Loosing a race is like loosing xp and coins.
-Drive safe!!