In order to give your plant's roots plenty of air, make sure you keep the bottom of the planter is off the ground. Don't let them sit on a flat surface so that the the drainage holes will be blocked (This cannot happen with our planters). Never let your plants stand in water.
If you live in a humid area or get a lot of rain, you should consider planters that are made of a porous material, such as wood or terracotta. A porous planter improves air circulation by pulling water out of soggy soil. The downside of this is that the container will dry out more quickly, which means, if you live in a drier area you will need to water more.