Subject: how do I do simple incubation

we are taking saliva samples and don't know how to incubate them after they 
have been transferred to the petri dishes.  its for a science fair 
experiment.  Don't have much time or $ for materials - we think that wrapping 
the petri dishes in a towel and putting them in a dark place for 24 to 48 
hours is enough but not sure.  We have blood agar petri dishes and sterile 
swabs for the experiment, are ready to go but are afraid to continue until we 
know how to incubate. We tried once with regular agar but the experiment 
didn't work, agar too thin, and didn't know we needed to incubate it.

Re: how do I do simple incubation