Besides describing the Blakes Hitch used for tree climbing, this post reveals two principles of my approach to knot tying: 1) use the contour of your hand 2) how you hold the two ropes on the first step is important.
Here's the recipe for tying the Blakes hitch. Wrap around your thumb twice. Wrap off of your thumb twice. Pull the rope across the coils placing it over the bridge. Wrap in the opposite direction around the climbing rope. Finally reeve the end of the rope between the 2nd and 3rd coil. Use a fisherman as a back-up
Here's a video for you: http://www.youtube.com/watch?v=8twEso5I1jE