Plastic string, or gimp, is a great crafting tool that comes in a few different varieties. Most are either flat or round; some are stretchy. For this braiding project, start by using the flat gimp. It will be easier to work with since you will be making a box stitch lanyard. Projects like this go by many other names, like "scoubidou" and "boondoggle," and there are many other patterns to try. The box stitch is an easy beginner's stitch.
Cut one strand of gimp from each skein. Decide now how long you want your lanyard to be--about 14 inches of gimp is equal to 1 inch of finished lanyard.
Cross one strand over the other at right angles. Hold the cross firmly with your thumb and pick up one of the strands opposite you. To make this easy, call the vertical strand "white" and the horizontal strand "black." Cross the white strand over the middle and hold it in place. Pick up the other white strand and cross it over the opposite direction.
Pick up the black strand on the right. Cross it over the white strand close to it and under the second one. Pick up the other black strand and cross it over the first white strand and under the second one. You should have the beginnings of a knot. Pull the end of each strand until the knot is pulled fast and you have a checkered square with white and black diagonal from one another.
Use the same method of looping two of one color over the middle knot and then weaving the opposite color through until you have used up all the gimp. Tie the loose ends in a knot and attach your hook or key ring to one end to finish the piece.