What precautions should I take when preparing food while I have a cold?
Wash your hands thoroughly and frequently.  See Clean Hands Save Lives.
Do not at any point cough into your hands.  Coughing into a sleeve is considered less likely to transmit germs.
To really prevent breathing on your food and potentially transmitting germs that way, you could consider wearing a mask.  


Personally I'd consider the last step optional (and the other two not).