Use one lens.
Yes, it can be frustrating at first and you’ll fret over the shots you miss, but sticking with just one lens on your camera for a period of time lets you learn it better than anything else. I’ve been obsessed with my 85mm f/1.8 lately, and it’s been all I’ve shot with outside of music photography. It’s a bit of a pain in that I have to be ten feet away to get a decent shot, but you know what? I know now how many steps away I need to be with that lens to get a head-and-shoulders shot, or how much further back to go for a full-length shot of a kid playing in the backyard. I don’t have to think much about it. I walk, turn around, and the shot is there to be framed up.
I think it was on the original “X-Files” movie DVD that there was a behind the scenes featurette where someone was marvelling over Martin Landau. He asked the director what lens was attached to the camera, and then he pointed out exactly how much of his body was in the frame. He knew that the 50mm lens on the camera six feet away meant that his head, shoulders, and collarbone would be visible and nothing else. He had been around enough movie sets to know that.
Now I know a little of that feeling.
The other nice thing: When I put the 28mm lens on my camera now, it seeems ultra-wide by comparison. =)