do:
keep your tires clean and pumped up (rule #1, will solve most problems)
use tubes from a bike shop, not shitty ones from Wal-Mart
nice belted tire (conti gatorskin, specialized armadillo, or similar)
try and ride on clean roads when possible
latex sealant such as Stan's or Caffe (overkill IMO, I don't use it, but you will never get a flat with this stuff)
don't:
tire liners, at least for me not worth the hassle of keeping one more thing lined up when you install a tube
those nasty "slime" tubes, don't work too well and are hella messy
abuse the valve stem