In terms of cuing, focus on keeping your head still, your stance and bridge as stable and symetrical as possible, and hold your breath on the stroke like you would firing a rifle. If you need to learn about screw/english, just look on you tube and there are lots of videos explaing the key principles in terms of how it will respond from balls and rails.
In terms of amateur strategy, in eight ball you frequently have positions/shots that appear strong but are actually very weak. The most fundamental mistakes in this regard are usually potting simple balls when hard ones are left, potting balls over pockets prematurely, and thinking that having fewer balls on he table puts you ahead.
Every ball you sink in 8 ball makes your opponent's life easier - particularly balls blocking pockets etc - and as a result, often moving difficult balls out/playing safe (these two things can often be combined) is a better tactic until the game is more open and runs of balls can be made easily. Don't ever think of the game as whoever has the most balls on the table is behind - one of the best hustles in eight ball is to give a weak player all 7 of their balls off the table and simply snooker them/clear up on a table full of options for you and none for them.
9 ball at the amateur level is a game that requires a sound knowledge of the runs of balls you and your opponent is capable of, and to approach the game very defensively until a spot arises where you feel happy clearing up, or you feel that your opponent can and that you have to go for it as a result. In these situations all out attack is required. Try and look at nine ball as a game of two polar opposite gears - all out defense and all out attack. Don't just pot balls aimlessly without a plan for the nine or a future safety shot.
Also, don't forget the three foul rule either - it is a great tool against mid level players in the early stages of a game where snookers are easy to set due to the number of balls on the table.
And practice, practice, practice - it is the only true way to get good.
edit -
some instructional vid series that looks ok for the basics of cuing/ball control.
Last edited by Wamy Einehouse; 08-18-2010 at 01:43 PM.