I am planning to do astronomy nights at local schools etc for the International Year of Astronomy.
In my opinion these are best done just before first quarter moon because kids can see the moon (but it is not too bright) and some deep sky objects in rural areas.
http://aa.usno.navy.mil/cgi-bin/aa_m...r=2009&ZZZ=END
It is also best to pick months when it is more likely to be clear in your part of the world.
http://www.bom.gov.au/climate/averages/
Look at the ratio of clear days to cloudy days.