To get lots of NOS easily, when you are standing still hold hand brake (R). Next, hold the gas then hold Left or Right. You should spin around and create smoke. This should give you 300 points instantly to recover turbo boost

Get on the highway and drive in reverse. After a few seconds you should begin racking up points on the right side of your screen. These points will give you extra NOS. Note: Crashing into traffic at high speeds will reduce your NOS.

When you are on the ground, activate hydros and keep flicking the Left Analog-stick Left repeatedly to get lots of points for filling your NOS bar. You can also do about three donuts, then wait and do another three donuts.