There is no realy way of teaching how to drift with NOS but here are some points I can give you for some information.
1.)
Practice - Everyone will say this because it's true! Practice is the biggest tip I/anyone can give you. Aferall, practice makes perfect.
2.)
Patience - You won't be able to learn overnight,, you may be able to pick up the basics but you won't be perfect at it straight away. As I said above - practice makes perfect
3.)
Drift in various places - People will say /drift1 and others will say /lvap. I agree they "can" help but they will only get you so far. You should regularly go through all the drift teleports and drift on the streets.
For the basics just practice basic corners. For the start personally done /lvap around the runway. The corners are bigger and longer so you need to know when to use the throttle and when to ease of more than at /drift1 (In my opinion).
If you have any problems or anything just say and I'll happily help.