drink PLENTY of water. lots. A lot of people say "I drink tons of water" but almost no one actually does.
For the record, healthy men should drink about 3 Liters of beverage (water or whatever) in a day, and healthy, non-pregnant women should get 2.2 Liters. Illness increases your body's demand for hydration, and better hydration also helps your body fight off illness (this does not apply to some kidney, liver, adrenal, and heart diseases, which may actually be exacerbated by excess water intake).
Water helps keep the mucus more viscous, and then it drains easier/is easier to clear out. This only helps, but it's a great idea in general anyway.
I pick up some Claritin (does not cause drowsiness) for allergies, Claritin-D if I want the decongestant component... because if it's already there and you don't dry it up, it's just going to sit there.