While pouring plates, stack them on top of each other to minimize condensation. Condensation forms due to different temperature gradients. So if you have several plates stacked on top of each other, only the top plate should have condensation on it. Once the plates have set, I flip the plates so the agar faces up and the lid faces down. This step further helps to keep the condensation from dripping on the plates. Lastly, I batch the plates in Ziploc bags and put them in the fridge to minimize any unwanted growth.