Drifting in 10 Steps:
1 - Forget your experience of any earlier game you tried to drift. I drifted on dozen of another games and my background experience came more to confuse than help my experience on first stages. So clean your mind first, then go to the tracks. I say that because every game have it own phisics, tricks and setups... so unless you drifted in a game really superior than Gran Turismo 5 (i.e. R-Factor), you will bring bad habits to the game.
2 - Before pick a car and work on drift lines and setups, go back to the basics and tune your device. DS3 or Racing Wheel? Analog or D-Pad for turning? Buttons or Triggers for accel and brake? Its all personal to you, except the standards: All Assists Off and ABS between 1 to 3. Racing lines? Unless you´re in a custom track that you dont know the corners, keep it off too.
3 - People say you must get first a low powered car, but they dont specify if its stock or tunned. Also probably you will not have so many idea how to setup your car properly. So i suggest you start with a well known stock car and train with it, respecting its limits. You will not have a complete D1GP performance, you will miss so many links, but at least you will understand how to make a car lose its grip and how to control it. A maxxed car will lose its grip by itself, so first u must learn to create the drift instead control it.
4 - For several reasons, use Confort Hard Tires always. Don´t be another troll in a multiplayer room.
5 - Tunning is a very personal thing, depends really of the device and style of your driving. Will not be easy to figure out what every thing do (even the most experienced drifters on GT5 have their doubts sometimes). Anyway when everything fails, you can appeal for the Drift Setup Depot section from this forum. If the car is not responding as you wish, don´t blame the car and work hard on it. Right now i do have almost 100 cars finetuned for drifting and i love them all, but at start before i be worried of collect and put on sideways massively, i got worried to at least have one beast to sharp my techniques, then move to another car and so on.
6 - Drifting score doesn´t matter so much, specialy if you plan to be a good e-drifter. Sometimes, a lap with bad lines can make more points than a good lap doing everything right. Also, the drift score scheme penalize extreme high angles, i.e. a reverse entry. So if you are training alone, its better go to time trial and drift using your ghost as sparing than go do drift mode and farm some points. Plus, drift score doesn´t gives money, so exept by the cheap PS Drift Trophy (10k in a sectioned lap), all the rest is useless.
7 - Start training on Tsukuba only, mostly because 99% of the roms you will find on multiplayer will run this drift box. Domain all the 9 links.
Suggested video, starts at 2:50.
8 - After domain Tsukuba while solo and pratice a lot of tandem with your ghost, you are ready to try your luck on multiplayer without be a shame. Keep your mind opened and learn the principles of the tandem, learn how to keep your position, how to dose your atacks while behind using angle and breaking control, learn how to drift based on your partner´s line. Be aware that the online physics are slightly different than the solo physics. So its wise to finish your finetune while inside a multiplayer room.
9 - Bored of Tsukuba? Ok, so i have another suggestions for you, for diferent exercises.
Tandem mastering: Suzuka East
High Speed Drift mastering: Trial Mountain Reverse
Banked Corners mastering: Eiger Short
10 - Don´t quit easy. If drifting mastering would be cheap, people would lose its interesting in few weeks, and thats not what happen on GT5. As myself, i know many people that play this game with the only purpose of drift online, and the best drifters in the game are always learning something new.
. i love it and i love GT 5 , even more so than forza 3 which is supposedly a better game.
) , then after that all i'd suggest is practice on a smaller track like Autumn ring mini reverse or Tsukuba , then you can work your way up from slow speed drifting to the faster stuff 
