Similar to playing an instrument, Knot tying is a skill that is developed over time with much practice. It's one of those skills that you don't know you need until you find yourself hiking in the woods and want to tie up a temporary shelter with something other than a basic bow knot used for tying your shoes.
The next best thing to finding an old salt to show you the ropes is an iPad app, Knot Guide HD from WinkPass Creations. Knot Guide HD has 95 knots that are organized into 17 different categories. There are 83 unique knots and a handful that are variations. You can view the knots via categories, alphabetically, or a customizable favorites list. You can even search if you know the name of a knot.