Neti pot twice a day. Black tea with ground ginger. Chapstick on the nose (I really hate a raw nose). Wash hands frequently.
Dissolve menthol cough drops in hot water and drink - works much better than sucking on cough drops.
Airborne anyone? 
My mom gives me a thing of it every fall, insists that it will stop a cold dead in its tracks. I try to tell her that my Immune System of Doom (for any poor pathetic virus that tries to invade my body, that is) is sufficient (I’m around little kids all day), but she always insists.
In addition to the excellent suggestions already given, try sleeping (when you do) on your side with your head elevated as high as possible. I use three pillows.
Aleve Cold & Sinus if you just have an annoying head cold. It has 12 hour sudafed which is great; no taking crap every 4 hours.
-If you have a chest cold or a headache too, Alka Seltzer cough and cold tabs, which has decongestants and antihistamine (Dayquill does not have the latter). These are liqui-caps/tabs, not drop-in-the-water-fizzy stuff. They’re new.
-Target brand extra soft tissues or Kleenex extra soft.
-Dr Bronner liquid Peppermint soap in the bath if it’s really bad.
-Remain elevated when sleeping to better drain.
-If you have something HUGE to do at work or school and literally MUST function, Afrin to clean your head and sinuses right the fuck out. Used it for a physics final in college.
-For prevention: sanitizing wipes (Lyson, clorox, generic) on door knobs, light switches, etc and sleep and hand washing.
I don’t respond well (to put it mildly) to the usual cold medicines, so I mostly muddle through with a neti pot, hot showers, a steady supply of mint tea (hot and extra-sweet), and as much sleep as I can manage. The showers and the neti pot mostly keep the congestion under control, and the tea keeps my throat from getting raw.
If the congestion gets really bad, I’ll sometimes take pseudoephedrine and deal with the side effects as best I can.
I don’t really do much of anything, except brace myself that the next two days are going to suck. If I’m feeling really congested though, I will eat some spicy food, which I don’t normally do.
For me, eternal vigilance seems a bit extreme given that all I’m avoiding is two crappy days every year and a half.
I just take a cough syrup that has dextromethorphan but not guaifenisin. The former keeps coughing fits to a minimum, the latter gives me hives. Unfortunately for me, damned near all of the cold medicines I see on shelves these days contain guaifenisin.
Sleep. Lots and lots of sleep. And hot soaks in the tub.
Just beginning to get over my second cold of the season. I can usually keep recovery inside of a week if I keep it out of my chest. Usually, that means the AlkaSelzer soft gels (day and night package) for the first couple of days and an antihistimine after that, VapoRub, switch from coffee to hot tea (I drink milk in coffee…not so good with mucas issues), SF menthol cough drops, lotion tissues, lots of soup and most of all, plenty of rest / sleep.
This time out, I burned a couple of sick days to stay home and take care of myself. The crud is almost run its course and not in my chest, so it’s off to work tomorrow.
Knudsen’s makes a “Lemon Ginger Echinacea” juice. It’s kind of like spicy lemonade. My favorite remedy is to heat up a glass of that in the microwave. Clears the sinuses and helps me sleep.
Echoing thoes that said zinc. Lots of zinc. Zicam is the best stuff ever. (& if you can’t take the lozenges, try the nasal gel.)
I use a neti pot at the first sign of snot build-up or when I’ve been exposed to lots of things that irritate my sinuses.
When folks start getting sick anywhere near me, I up my hand-washing routine and avoid touching my face moreso than usual. (Wearing makeup helps this for me, but may not be practical for everyone.)
When I start to feel even the slightest “I might be sick soon” feeling, I eat a whole clove of raw garlic, gargle with salt water, and occasionally a hot toddy. I’ll also consume some unpasteurized honey at some point, and ward off vampires from the insane garlic smell I will now emit for the next 24 hours. If I keep it up, I tend to kill or reduce the incidence of any sickness to significantly less than the duration of the sickness that the person who gave it to me. I also will either wash my hands or sanitize them every time I blow my nose if I am in contact with other folks, and wipe down my work surfaces with Lysol or some other sanitizing solution to kill germs so I don’t reinfect myself.