Make sure the four strands are perfectly even. The best way to do this with hair is to divide the portion in half, and then divide each half in half. If you are using yarn or any material other than a person's hair, make sure that the tops of the strands are secured; this will help you gain proper tension throughout the braid.
Hold the strand farthest to the right in your right hand; hold the other three in your left.
The basic rule to any braid is to take one strand at a time and alternate taking it over and under the others. Take the strand in your right hand and take it over the first strand in you left. The strand that was in your left hand should now be in your right. Hold it securely to your palm with your thumb.
Use the available fingers of your right hand to continue the over/under pattern.
Repeat Steps 1-4. Make sure you keep even tension throughout the braid. It may help to gently tug down on the braid. However, do not use too much force.