This one is just easy, but if you're sick let folks know. It shouldn't be an issue to cancel game, nor is it going to get you shunned or anything. It is however important for other people to know, and if enough people are sick then the GM may actually want to consider calling game off. Either way, you being sick can do more than just inconvenience you, it can make people miss work if they get sick and they have a right to know they're getting into that situation.
2. Wash Your Hands Regularly And Thoroughly
This is another easy one, and something most of us are doing all the time anyhow - or at least I hope so - but there is a reason so much advice focuses on keeping your hands clean. Hands are a great way to spread germs, and think of all the things you are touching that your fellow gamers are also touching all the time. Keep your hands clean and you'll do a whole lot better for yourself.
3. Bring Your Own Dice
Speaking of hands, bring your own dice. This is already a rule for some game places but others are more lax. Specifically around here we have a lot of people sharing dice - heck, we have a communal dice jar for our table. Sharing is awesome, but if someone is sick - and you're not - you are only going to improve your chances of staying healthy by having dice that only you touch.
4. Basic Manners
Back to the basics, but you'd be surprised how easily they can be forgotten. If you are going to cough cover your mouth and try to use your elbow or upper arm instead of your hand. Why? Because you're going to use your hand to grab things and touch people. If you do end up coughing into your hands, wash them. If you are sick, try to keep your hands to yourself as much as possible.
5. Other Tips?
Does anyone else have other advice to add? Sound off in the comments.