Hickey, just some sharing..
Few types of slapping...(many more i guess)
1. Tradition ones use the bone part of your thumb..ur bone tt protrude out(shd b able to feel it).Some hit on the last fret or slightly after the last fret. Of cos u can hit anywhere that u thk is the best tone. Those that use lot of strength type are probably pple like Flea, Louis Johnson aka Thunder thumb. Vail Johnson looks quite relax to me, but can go very fast.. Same as Mark King (cool ring), their fast slap need lots of endurance. Can check out Stu Hamm, Chuck Rainey, John Entwistle, Dave Larue, Anthony Vitti,Armand Sabal Lecco, Stanley Clarke, Marcus Miller and Larry Graham also.
2. Snap type you can check out Abraham Laboriel. He also uses his palm to thump the bass..Very accurate. You can try using your fingers to slap as well if u like.
3. Follow through type you can check out Victor Wooten. When he slap, e.g on the E string, it will rest on the A string(so if he wan to do double thumb can easily come up). Marcus miller prob does that when he uses his double thumb stuff.
The trick of hitting just the note you want also involve your left hand muting the strings that you don't wan it to sound. You can practice accuracy by alternating the string. ie. slap on E than on D string than slap on A followed by G string. Practice open string, noted string, muted string and etc.
After getting the accuracy, you can practice basic rhythmic pattern i.e drum pattern.
The release part which our fren mentioned earlier is after you slap (or bounce) you dun stick ur thumb on the fret but sort of bounce back. that is prob wat he meant by release?
Dave Crigger once mentioned that it is like u r touching something hot and quickly move back.
Btw, we only discuss about slapping.. havent cover popping, left hand slap and etc..
Have fun..
Cheers,
Ben