Nothing! It's normal! (Okay, so I'll mist them as often as I get a chance, and try to get them wet when I water. That's all optional, though.) Really, the roots will tend to grow toward wherever they are happy.
If you have lots of roots growing out of the pot, that can be a cause for concern. If you notice almost all the new roots growing out of the pot and avoiding the potting mix, that can be a sign that the potting mix has broken down, or that you're overwatering; either way the roots won't be happy in the pot. If this is happening, it's best to repot right away. (If you've been overwatering, also water less often or repot into a coarser mix.)
The other time you'll see very many aerial roots is if the plant has grown over the edge of the pot. If this happens, it's a good idea to repot the next time you see new roots starting to grow.
Most of the time, though, a few roots growing out of the pot is normal and not a concern: in fact it can be a sign of good health!
