I think I've been lucky in working with some very, very good spin coaches, and there are a few fundamentals that they work on. At the point of delivery, your back leg will be crucial. The best bit of advice I was given regarding this is to imagine your back leg is stepping over a low brick wall - this will ensure that you get the height at the point of delivery, and also convert the run up (which often is completely useless), directly into revs on the ball.
The other thing, is to make sure you pivot after releasing the ball. Most amateur spinners just bowl and stay front on, whereas if you bowl the ball and then pivot around your front leg you will end up getting into a better position to field off your own bowling, but also you will put a lot more "action" on the ball.
And of course, the front arm is essential too.
Generally, the pace and dip and drift comes from the "action" on the ball, and this is generated in the run up from the front leg, and also the pivot after you've released the ball. That's what's worked for me in the past! Hope it helps!