Tip #1, High action. I mean so high you can barely fret a note.
Tip #2, obscenely heavy strings. .12's at least.
(If at all possible, a guitar set up specifically for slide is best)
Tip #3, Take your guitar pick firmly in your right hand, and throw it as far as you can. Your slide playing will improve dramatically from fingerpicking, as it allows you to easily mute strings you're not playing.
Tip #4, If that was your only guitar pick, go get it, you might need it for your other guitar, and I don't want you blaming me for not having it.
Tip #5, Try tuning your guitar to an open chord. I'm partial to Open E or Em, Open A or Am, and occasionally a little D.
Tip #6, put your slide on any finger OTHER than your index finger. This allows you to mute the strings behind the slide to eliminate noise. As with tip #3, a clean technique will be an instant improvement.
Tip #7, Choose your weapon wisely young jedi. A steel slide will produce a brighter tone than glass, glass produces a warm tone, but is a bit brighter than ceramic, and finally a ceramic slide will produce a very warm tone. Just don't use a ceramic slide on a Les Paul. Sounds like poop.
Tip #8, Experiment, play with your guitar on your lap, use a lap steel bar instead of a slide on your finger, hell, try playing slide with a Floyd Rose bridge.
Tip #9, Practice hitting your "target" notes. One of the biggest reasons beginning players sound awful is because they spend so much time trying to land on a note.
Tip #10, When in doubt, slide into a note from a lower pitchThe human ear is much more likely to recognise a dissidant note that is too high in pitch.
Tip #11, Vibrato, vibrato, vibrato! I prefer a shallow, but very slow vibrato when I play slide, as opposed to an extremely wide vibrato when fretting.
Tip #12, Have a look at
Warren Haynes video, Electric Blues and Slide Guitar, if you PM me with your email, I even have a lesson on the slide playing of the late, great Duane Allman.
Tip #13,Expose yourself. Not like that, put that away. Expose yourself to different slide players. Duane Allman, Warren Haynes, Derek Trucks, Bonnie Raitt, and
David Gilmour to name a few.
Tip #14,Once you've managed to incorporate all these tips into your slide playing, forget everything I just told you and develop your own voice. THAT is the key to playing slide. Its the individual nuances that make great slide players.