Well, lemme tell ya a lil' story.
After one jam session with my band (I didn't practice for a while so I was kinda goin in fresh) my middle finger got this huge, painful, blister on it. So, like always after a good jammin', I want to practice over stuff learned. So I started using my index and ring finger to play. After the middle finger healed, I used it as normal and the ring finger. It was all awkward at first, but I got the hang of it. So, for fast playing, I do the 123 pattern. When I'm just groovin', I use the ring finger whenever it feels right. Sometimes I'll just use the index and ring. So for me, it just came about by fortune that I started using 3 fingers. The 3 finger thing is good for fast playing.....real good for fast playing, you just have to keep a good head about how many notes you're playing and not get ahead of yourself (it can get slightly confusing at times and you'll end up playing extra notes).
I guess for practice, you could just do what I did and introduce the ring finger to the line up by just using the index and ring finger every once and a while. Or you can just use all 3 and get the feel of it faster. However you decide. I don't have any "actual" warm ups or anything, so those were my suggestions. Hope they help.
