I get colds way too easy. what's the best way to prevent catching viruses when training hard?

What virus?: Among the thousands of potential pathogens are the viruses which cause the common cold, and influenza viruses and their cousins. The best thing to do is to keep away from people who have these, get immunized for influenza yearly, wash your hands after touching people. Training hard has nothing to do with it.

Train alone.: You don't catch colds from training; you catch colds from training with people, specifically people who are sick and coughing and spreading their viruses and germs throughout the gym. If you don't want to get sick when training, train alone.