I've been playing slide for years, as I got into old Delta blues as a youngster, and was a fan of Duane Allman and later Ron Wood. Starting out tuned to E is a good idea, and then, try other tunings. I've been using open A for electric and open G for acoustic lately. I can't play pretty slide guitar like George Harrison did no matter how hard I try, and I can't play slide in standard tuning. It has to be an open tuning. I'm shocked at the number of guitarists I know and work with who can't play slide at all. I call my style of slide playing, "slash & burn." Think Hound Dog Taylor and Elmore James.
I don't play slide on standard low action guitars, because I hit the strings hard, so I have quite a few dedicated slide guitars with high action, including a '58 Supro Belmont, three 60s Japanese electrics (which are almost perfect for my needs, because they sound so dirty with OD added), plus a Guitar Fetish Slick SL-59 with one P90 (it looks like an old Melody Maker). Lately, I've been using my '95 MIJ Candy Apple Red Strat, which is working out nicely. On the acoustic side, I have a 1929 National Triloian, a 50's wood body Regal, and a Hohner Triolian knockoff. (Edit: that I have since sold).
When playing clean on electric, I usually add some compression, which gives me that Lowell George vibe. I have many slides; brass, steel and glass. I have never found a ceramic slide that fits my finger nicely, but I'm sure they're out there.
