one of the first things i learned how to do was "read" waveforms and cut single sounds and loops. i didn't really have anything but a simple wave editor, so i spent a lot of time practicing cutting samples and loops perfectly, sans click.

another little tip:

if you are cutting loops in a wav editor, and you still can't manage to eradicate the click at the end, do a short fade out at the end of the loop. make it subtle enough that it doesn't sound like a volume dip. if u do this right, it really helps your loops come out clean when they ARE looped in a sequencer...