If you are using a camera with autofocus you need to be mindful of what you are focusing on because many autofocus cameras try to focus on the center of the frame. Most autofocus cameras have a two-stage shutter button. This means you can press and hold the shutter button halfway down to focus on what you have in the center of the frame, then recompose the shot before depressing it fully.

Adapted from Hot Shots: Tips and Tricks for taking better pictures by Kevin Meredith (Chronicle Books, 2009;$17)