In the Store: Always hold a camera before buying. How it feels in hand is as important to the shooting experience as its list of features.
Pad your budget to include a high-capacity memory card. The tiny cards that most cameras ship with are virtually useless for storing the large files created by today's high-res sensors.
Don't obsess over megapixels. Image quality is determined as much by sensor size (the bigger, the better), lens quality, and the quality of the internal software.
In the Field: Your battery will die just when the elephants appear. Always carry a spare, and keep it close to your body in cold weather.
Changing lenses? Be careful not to let dust get on the image sensor. Clean it with a blower brush if it gets dirty.
At Home: Don't let your images turn into the digital version of a box full of slides. Organize them on your desktop as soon as you get home, and start each trip with an empty memory card.