Instructions
Identify the location where the arrowhead was found. If you know the state or region where the arrowhead is from, that will narrow the list of possible projectile points from 1,200 to a couple of hundred options.
Identify the material the arrowhead is made out of if you don't know the region it came from. Chert, for example, is native to the Illinois and Missouri area.
Determine the overall shape of the arrowhead. For example, is it stemmed, stemless or notched? If it's stemmed, note the shape of the stem; stemless, whether it's fluted or not; notched, whether it's notched in the side or from the corner. The location and the design of the arrowhead is enough to narrow the type to only a dozen possibilities.
Consult a book that specializes in the projectile points from your area to cross-check your arrowhead with already identified ones. "Arrowheads &Stone Artifacts: A Practical Guide for the Surface Collector and Amateur Archaeologist" by C. G. Yeager is a classic. Two other options are "Arrowheads and Projectile Points" by Lar Hothem and "The Official Overstreet Identification and Price Guide to Indian Arrowheads" by Robert M. Overstreet.