For over-the-wrist spin, grip the ball so that the seam runs across the first joint of the index finger and the first joint of the third finger. For the leg-break, and the over-spinner or top-spinner, the ball is spun off the third finger. The wrist is cocked, but definitely not stiffly cocked which would prevent flexibility. In delivering the ball, you look at the spot on the pitch on which you wish the ball to land, your bowling hand starts level with your face and then describes what could loosely be termed an anti-clockwise circle to the point of delivery.
The position of the bowling hand dictates in which direction the ball will spin. At the moment of delivery, the positioning of the hand is as follows:
Leg-break
In delivery, the back of the hand is facing the face. (The ball will spin out with the seam rotating in an anti-clockwise direction towards slip.)
Over-spinner or top-spinner
In delivery, the back of the hand is facing the sky and then the batsman. (The ball will spin out with the seam rotating in an anti-clockwise direction and towards the batsman)
Wrong'un
In delivery, the back of the hand is first facing the sky and then the ground. (The ball will spin out with the seam rotating in an anti-clockwise direction towards fine-leg)
You should practise the hard-spun leg-break 90% of the time, the variations only 10%. You should be side-on to the batsman and looking over your front shoulder as you deliver the ball and then your bowling hand will finish up going past your front thigh. This means, if you have done it correctly, your body will have pivoted and rotated anti-clockwise. This 'pivot' is of great importance. If you bowl a ball that is too short, you can be almost certain it happened because your body was 'chest-on' to the batsman, rather than side-on, and you dragged the ball down into the pitch. When you are bowling in a net, make a white shoe cleaner mark the size of a 20 cent piece, on what seems to you to be a good length - that is, with the leg-break pitching where you would not like it to land if you were batting.
Never have your bowling arm at or past the perpendicular when you deliver the ball; it should be at least a few inches lower than the perpendicular.
Don't even think about learning the 'flipper' before you have mastered the leg-break, top-spinner and wrong'un.
Keep it simple
Attend to the basics first (focusing on the five points listed below); if you can't do that, then the more complicated things will be impossible anyway. It is possible to extend some of those points but the one thing of which you can be guaranteed is that common sense will always outweigh rhetoric and complication.
1. Patience: bowling is a tough game and you will need to work on a batsman with your stock ball, sometimes for several overs, before putting your plan into action. It may not work the first time or even the second. (If you take a wicket on average every 10 overs in Test cricket, you will have a better strike-rate than any of O'Reilly, Grimmett, or Warne. If you take a wicket on average every eight overs, you could have the best strike-rate of any modern-day Test bowler, fast or slow)
2. Concentration: anything less than 100% concentration running into bowl is unpardonable. The spot on the pitch where you want the ball to land should be the most important thing in your mind from the moment you turn at your bowling mark. (If someone offered you $10,000 if you could throw a ball and hit an object 19 yards away, in trying to win the money would you, as you were throwing, look at someone standing nearby, or at some other object?)
3. Economy: this game is a war between you and the batsmen. (Is there some very good reason you want to allow him more than two runs an over, thus possibly giving your captain the idea you should be taken off?)
4. Attitude: calm, purposeful aggression and a clear mind are needed, plus a steely resolve that no batsman will get the better of you over a long period of time. Always remember as well that cricket is a game to be enjoyed and that you are responsible at all times for ensuring that play is conducted within the spirit of the game, as well as within the Laws. (In other walks of life, you will want to be mentally strong and on top of the opposition. Is there some particular reason why, within the spirit of the game, this should not be the case in your battle with the batsmen?)
5. Practice: all practice should be undertaken with a purpose. (You think hard before doing most other things, why should you allow cricket practice to be dull and boring?)