Influenza is spread by aerosolized droplets, direct contact with droplets, and sticking your contaminated fingers up your nose... seriously! Don't pick your nose.

Colds are transmitted by inhaling some infected person's mucous when they cough or sneeze or touch a surface that has the cold virus on it, then sticking your fingers in your nose or eye. I'd guess I've had a ton of colds because I had an itchy eye. If you think about it, you wash your hands, and then touch the knob on the sink, the door to get out of the loo, some surface such as a desk, counter, phone, or anything, and your hands are re-contaminated. I personally believe keeping your hands away from your face is probably the most effect thing you can do to prevent colds, but frequent hand washing is good. Plus, it prevents transmission of a lot of other things.