1: Get (and maintain!) sealants. They minimize wear/tear and cavities. Get them even if insurance doesn't cover it -- they're not that expensive. They block up all the little crevices where cavities start. They usually only last a couple years though so make sure you get them redone when needed.
2: Use a flouride rinse. Flouride rinses are the only thing that actually help your teeth remineralize and can actually repair small cavities. Don't eat for 30 minutes after gargling.
When I first moved to Maryland, I got cavities for the first time in decades all because I started using a water filter that strained out all the flouride. My dentist recommended the rinse. No new cavities since (in over a decade). Mouthwashes are different than fluoride rinses; be sure you get the right thing -- it should contain 0.25% fluoride ion.
3: Floss. Every day. A woven floss is better than waxed or teflon floss -- the woven stuff cleans more completely. It feels amazing, you can actually feel the difference.
4: Do not chew ice. You may be able to see cracks in your teeth -- hairline fractures from years of abuse with a flashlight. This is depressing, but not necessarily a problem, just don't keep pushing your luck.
This goes for more than just ice. Don't chew on any hard objects (ice, pens, pencils, hard candy, clothing tags, your nails, or anything brittle). My dentist said that's the number one reason people crack teeth. Same goes for animals too -- it's not a great idea to let them chew on ice.
It's also not great to clench your jaw or grind your teeth -- if you do, see your dentist for a mouth guard or advice on behavioral training (or just, like, be under less stress :).
5: Get an electric toothbrush. It's not just hype. After this incident, I went a YEAR without setting foot in the dentist's office because I was too traumatized to even think of getting back in that chair. When I finally made myself go, I thought my teeth would be in terrible shape but they weren't. I was told they looked like I'd just had a cleaning.
Brand doesn't matter but quality does. Buy a professional electric toothbrush, not the cheap supermarket kind for under $20. A good electric toothbrush will likely cost $60-$80, although if you are strapped for cash, the cheapie powered toothbrushes are probably better than nothing.
Don't brush too hard because that'll make your gums recede. It actually takes very little force to get plaque off; you don't have to jam the toothbrush against your teeth and saw back and forth. Be gentle on your teeth and they'll be good to you back for years to come.
6. Ask for a "cervical collar" lead apron at the dentist next time you get an x-ray. X-ray exposure to your tissues is cumulative. This special apron will protect your thyroid. I don't know why it's not mandatory to give every patient this or why you have to ask but it seems like a good idea.