1. Tilt your cans from side to side. Do you hear or feel any water moving around in there? If you do, gently tip your can to pour out the excess liquid (be careful - don't let your soil and plants spill out as well!). 
  2. After draining excess water, use a toothpick to poke 1"-deep holes into the soil - this is called aerating and helps relieve drowning roots.