Atleast once per week use disinfectent wipes on door knobs, desk space (especially the computer keyboard), food area, and any other perpetually dirty or communal area. Germs cause many illnesses that can be easily avoided by simple cleaning. Disinfectent wipes are easy and effective, have your mom or dad send some up in a package, or hit up a local Target, Walmart, Kmart, CVS, grocery store, etc. Any of these places will for sure have these, and ladies, some come in scents that can make your college abode especially fresh.
Use Airborne and/or Emergen-C once a week, preferrably before going to bed on nights that you will be getting 8 or more hours of sleep. Twice a week is cool too. The main component here is the sleep, amp up your body with get better vitamins etc. and then rest on it, you'll wake-up feeling like a new person, even if you aren't sick. Emergen-C comes in Costco/Sam's Club size packs and various flavors so stock up.
When showering, be sure to use shower shoes. Communal bathrooms= bacteria, athlete's foot, warts, who knows, so don't take chances, wear shower sandals. Plus, if you shower before class in the morning, you already have shoes covered once you're out, so just throw on clothes.
This one might not apply to everyone, but, if you have a fridge, keep it clean. Food can get moldy and icky and before you know it you have food poisoning. So keep a little dixie cup, or something similar, in the fridge to keep it fresh and clean and throw out stuff if it's been in there for a while. Try and follow the one week rule, if it's been in there a week, you're probably not going to eat it, so throw it away and save yourself from the stench and/or sickness.