Running and Gunning - the amount of people I see play who cant run and gun properly is crazy! (Drill by: setting up a target 50 yds away, run one direction, shooting the target. When you reach the end of your run, turn and go the other way to practice both hands. Increase speed as your accuracy improves)
Sliding - again, the number of people I see not sliding properly, or even at all is a bit concerning... (Drill by: Simply sliding... duh)
To be honest mate, think of any element of the game - then know that you need to train in it... simple really.
Go to Robbo's Clinic in November! Theres a post somewhere on the forums (Announcements I believe) that will teach you a LOT!