I have a Morrell 6 string lap steel that I play from time to time.
And even though I've been playing slide guitar since I've been playing (26 years), making the switch to lap steel was a challenge.
The big things you'll want to pay attention to in learning slide/steel is intonation (where the steel or glass bar hits the strings so that it's in tune) and string muting (covering other strings that you don't want to be heard).
On a fretted guitar you place your finger right behind the fret to hit the note. When playing slide you place the bar right on top of the fret to hit the note. If you're behind the fret, you're flat...ahead of the fret and you're sharp.
Once you get the technique down to hitting the proper note then you incorporate the ability to go flat or sharp to your advantage for emotional playing.
Muting is super important. If you've got a 6 string steel and you only want to hit 1 note on 1 string, you'll need to find ways using your other fingers and palm (on both hands) to keep the other notes from ringing out. Muting can take a while to develop but it's key to controlled playing.
There's a lot of players to check out for reference: Sonny Landreth, Robert Randolf, Duane Allman from the Allman Bros, Ed King from Lynyrd Skynyrd, and a host of blues slide players that influenced the guys I mentioned above.
