1. Don't overdose on the polish. We've all been guilty on this - applying, removing, and reapplying nail polish x10 because it doesn't look right, painting nails without a base coat, or giving ourselves a manicure more than 3 times a month. The number one rule of healthy nails is always not to overdose on the polish. Too much nail polish can cause staining which leads to yellowing of the nails and also sensitive nails; neither is better than the other. To avoid this, limit your manicures to 2-3 times a month and apply a base coat to your nails every time you paint them. My personal favorite is the MAC Under Lacquer Base; it's more expensive than other drug store base coats, but definitely worth the investment.
2. Nail polish remover alert! Drugstore polish remover is absolutely fine, but next time you take a trip to CVS seeking a nail polish remover, ditch the dollar deals and opt for the more expensive - I use the Sally Hansen Polish Remover. Hey, it's only a dollar more.
3. Don't bite your nails. I know how hard it is to break this habit. Trust me, I was once a nail-biter myself. For me, it wasn't an effect of nervousness or unsettlement - I would find myself biting my nails at the oddest times, like when I'm updating Twitter. It took me an official 7 months to break (I still remember the day I realized I don't bite my nails anymore!) but it was well worth it. There are lots of ways out there, but the one that worked for me was the reward system. Everytime I didn't bite my nails for a week, I would go out to Pinkberry. For a month, I would go to the salon and get a fresh manicure. Just a little warning; make sure that the process doesn't accidentally empty out your wallet. (;
4. Take showers. Lots of them. And apply lotion directly after you get out of the shower, onto your nails (while they're still slightly damp). I have no idea why this works, and am too lazy to go research it, but it works. My nails always feel refreshed and renewed after an hour or two (these are times when my nails are bare and natural). I like to use Aveeno, although it doesn't really matter - just avoid strong-scented lotion. Oh, and one more thing: make sure you don't apply nail polish within 24 hours of your shower-lotion-healthy nails campaign. The feel-good refreshment disappears like poof, I warn you.
5. Grow them long, clip them short. Okay, so you obviously don't want uber long nails, but you also don't want super short, stubby nails, either. Grow out your nails (this will take a long time if you currently have stubby nails, but be patient - it's worth the wait!) and once they're pretty medium-long, clip them short again. Use your own preference for the length, but I recommend clipping them so you can still see a strip of grown nail. The picture at the very top of this post shows a super gorgeous floral manicure - pretty nails don't necessarily have to be long!