Here is a nice series of pictures of using the Montessori tying dressing frame.
Step one untie the bows and knots.
Step two open flaps of dressing frame and put one side back and pull back the ties, do the same for the other side.
Step three tie a knot.
Pull up middle of crossed over ribbons and pull through top ribbon.
This is a good place to stop for a first step. If your child is able, go on to making bows.
Step one-Place two fingers on middle of ribbon
Step two-make a bow around your two fingers.
Step three-loop the other ribbon loosly around the bow.
Step four-Pull folded white ribbon through the loop. Pull gently on both bows until secure.

If you are using shoes instead of the dressing frame just use two different colored shoe laces. Find ones that are thick as possible. Also, make sure they are the right length-not too short or too long.
Here are some more ideas-How to Tie Your Shoe