By ed2go Instructor Edward Burns
There are a few methods to consider for strumming through the strings of your guitar. If you’re using a guitar pick, grasp it between your thumb and index finger. Point it slightly upward when you down-strum, and use a very light stroke so the pick won’t get caught or hang up in the strings.
Another method is to use one or more of your fingernails. As you strum, just push your finger or fingers down and outward. Your sound will be thicker if you strum with two or even three fingers. This way, you get more than one nail surface raking across the strings. Use a very light stroke as you softly brush your nail (or nails) down through the strings.
When using your thumbnail for strumming, angle it so that it points slightly up. This way, when you down-strum, your thumbnail won’t get caught in the strings. Use a very light stroke, and softly brush your thumbnail down through the strings while rotating your wrist in a relaxed manner.
Edward Burns Teaches - Introduction to Guitar