You should head over to
Two Knotty Boys and watch the how to videos. They're very informative in that they go slow and actually show you knots in use.
If you start looking into shibari, you'll find that they use very few knots, in fact its mostly just overhand knots. So if you have a tough time with intricate knots, you can still do some pretty and functional bondage through simple shibari.
One knot I think everyone should know is the
mooring hitch. It's an easy way to tie off cuffs to a bedpost and although it can be undone by the person tying quickly, the bound person tugging won't undo the knot, just make it a little tighter.