The best way to learn to drift is practice practice and more practice.
When it comes to drifting throttle control is just if not more as important as your counter steer, like racing, everyone has their own style so try lots of different setups or tweaking until you find something you like.
If you are using a G25/27 I recommend using a manual clutch as clutch kicking can save you a lot of hassle and eliminate the task of a Scandinavian flick when need be.
I use 720 degrees for both racing and drifting, for me personally when I started I found it near impossible to pull off massive angle drifts right away, just drive as you would race and start kicking out the tail coming out of corners until you get enough skill to gradually increase the amount you can comfortably slide.
Mastering the art of drifting can greatly improve your race skills and evasive driving ability when things get a bit hectic.
I have attached my personal setup, it's different than most in that it is initially based off the characteristics of a soft sprung Arabian Drift setup, I have disabled the front brakes on it as I don't have a hand brake leaver so you may want to fix up the balance to your desire.
Happy drifting