I once worked with a woman who gnawed on a turkey leg while perched at the reception desk of a bank. This was wrong on many levels. Don't be her.
1. Keep it simple. If you eat at your desk, steer clear of foods that must be eaten with your hands. Also avoid food that requires deft coordination, such as spaghetti or anything eaten with chopsticks. Stick to sandwiches (wrapped in a napkin to avoid crumb-keyboard issues), small bite-sized dishes, or smoothies.
2. Shhhh. Don't chomp, talk with your mouth full, or chew with your mouth open. And by all means, don't answer the phone until you've swallowed.
3. Smells are bad. No odiferous foods. Period. Even if you think Kim Chee is the best-smelling food ever, the person two desks down may disagree. (Dude-across-the-aisle, I'm looking at you.) Be courteous and choose foods that don't waft through the office.
4. Be discreet. It gives a poor image to customers to see open take-out containers and dirty napkins all over the place. Even if you have no direct customer-contact, the last thing your co-workers want to stare at is a messy cubicle. Keep your mess contained, and dispose of it when done.
5. Company fridge. Throw out your leftovers. Seriously, what's wrong with you people? Heathens.
Above all else, use common sense. This is an office, not a Renn Faire.
Check out the rest of my articles, such as Bridging the Generation Gap!