http://www.animatedknots.com/

I use soft cotton rope that can be found in any hardware store, not coated with anything because that can cause slipping. As for preventing circulation loss and for turning a rope into ankle/wrist restraints, wrap the rope many times around the ankle/wrist instead of just once, neatly in a coil, without crossing it over itself. Also take care to make sure that no knots press against the skin, because that also can put pressure which could reduce circulation and cause discomfort (probably not the kind you want).

My personal favorite for tying ends of ropes to bedposts/bed frames is the constrictor knot, featured in my avatar It's easy to tie and does not slip.