Here is a trick that makes tying the Nail Knot easier. Use a short piece of plastic tubing instead of a nail or needle. You tie the not the same but when you feed the line back through the knot, you just slide it into the tube. Then withdraw the tube and tighten the knot. The tube allows you to wind the line tighter on the outside. A tube like that used on a WD-40 Can is just right but you need to shorten it.
Also in the FAQ is a question
that provides links to all of the needed knots used in fly fishing.