Good Hygiene. The only way to keep an infant from getting sick is by keeping them away from sick people. It is also very important to have everyone wash their hands well before touching the baby.
No prevention. Colds are spread person to person by mucous droplets. So the only way to prevent a cold is to not be around people who are sick, which is nearly impossible. But good hygiene can help. Don't go crazy with cleanliness. Its mostly about being exposed to others with a cold.
Avoid Crowds. The best way to minimize risk of infection in babies is to breastfeed. Any contacts with illness especially those with coughs or congestion are a risk. Snotty children are an even greater risk! Colds are typical for babies and for the most part self limited.