Design and performance
You should always try a camera before buying it. Make sure it fits comfortably in your hand and that it's not so big or heavy that you'll leave it at home. It should provide quick access to the most commonly used functions via buttons or other physical controls, and the menu system should be simply structured, logical, and easy to learn no matter how sophisticated the feature set.

A camera that takes longer than a second between shots (without the flash) makes action and candid photography very difficult. Furthermore, some cameras have long shutter delays between the moment you press the shutter release and the moment the shot is captured. Watch out for these long lag times as well as excessively slow camera start-up (more than a few seconds).