Welcome to the forum, and congratulations on getting what I think is the best film Leica ever.
Practice is the main thing, of course.
One focus trick some recommend is that you always return the lens to infinity when you stop shooting; that way, you only need to turn it one direction.
Another thing is to prefocus on where you know the subject will be, watch through the finder, and fire when the two images coincide.
A variant of that also works in lower light or with faster lenses; in a close situation, swaying your body slightly forward and back once you've set the focus can line up the two images much more quickly than twisting the focus ring back and forth.
With manual-focus SLRs, one generally needs to push the lens through the best focus, then slide back through and come back again to shoot. That is, you use the fact that the image is getting less sharp again as a sign you've overshot, and move back in a smaller step to see that you've got it. With a rangefinder, the coincident image is usually so sharply delineated that you don't focus back and forth, but bring the images into alignment once and fire. (My eyes aren't as good as when I learned that, but it's still a good rule to keep in mind. If it takes more than two seconds to focus, you're doing something wrong.)
Keep in mind also that the rangefinder has two windows. Because of the way the M5's speed knob is placed, it's easier to keep your fingers out of the way of the smaller one. But if a finger or the strap blocks the smaller window, the second image will disappear from the finder.
Enjoy the camera! Others will doubtless have their tips and probably some book recommendations as well.
Edited by ho_co, 19 January 2011 - 06:25.