The Hornsby Bend Bird Observatory provides an excellent presentation about shape recognition of Texas hawks in flight. The Cornell Lab of Ornithology All About Birds Guide and the Bird of North America website both provide detailed descriptions to help identify hawks.
Hawks are divided into two main types of raptors, buteos and accipiters. Buteos have long rounded wings and a wide short tail. They are known to soar over long distances without flapping their wings. They prefer to hunt in open areas where they can perch on a tall tree or pole and watch for their prey to move below. The red-tailed hawk and the rough-legged hawk are two examples of buteos.
Accipiters have short rounded wings and a long tail. Unlike the buteos, accipiters flap their wings several times before gliding through the air. They often frequent forested areas, weaving through trees and hunting smaller birds.