I learned a lot from studying this map:
http://www.boqueteweather.com/images...limate_map.jpg
The patterns keep repeating--what happens at different latitudes, differences between East/West coast of continents, effects of mountains, how jagged coastlines are more likely in areas of high rainfall (esp. w/glacier effect at high lats), etc.
This of course assumes Earth cosmology. Change size/distance from Sun, orbit shape/period, planetary size/composition/density (gravity), axis tilt, etc., then you have to make a lot of educated guesses, this might help:
http://www.cix.co.uk/%7Emorven/world...dex.html#intro