Watch the Licks and Solos online guitar lesson by TrueFire from Play Blues Guitar 7: Slide Approaches
Here you will learn some essential slide licks. Having these licks under your fingers can give you a nice batch of stuff to practice on as well as being licks you can pull out at the jam!
TIP! One thing that will make practice a lot more enjoyable, is if you are comfortable when you are practicing. Not necessarily "lounging in an easy chair" comfortable - but in a good relaxed position. Whether you are sitting or standing, make sure that you feel relaxed and your hands are in a good position. If you tend to tense up - then take some breaks and don't start back up until you feel relaxed. If practice is painful and no fun, how likely are you to keep at it? Not very. So get comfortable and your practice will pay off.