1) If your needle and snap will handle it, you might want to use 4 threads, that's two lengths of thread through the needle, hanging down on either side. Why not add a little extra security, eh?
2) Work just on the right side (RS). Trim the knotted end and position the snap above the knot to hide it, and keep the back side neat
3) When I finish sewing on the snap, I now run the (threaded) needle through the threads beneath the snap piece (the half of the snap I'm currently sewing to the garment). After I knot the end several times, I snip close to the knot right on top and bury it underneath the snap piece.
Here's a nice posting from Ashley's "Make it and Love it" blog, with lots of useful information about using and sewing snaps. Thanks Ashley!