Since everyone is posting their strategy, I guess I will too :)
I too stick to nerds to friends houses, cheaters to randoms castles. I never attack someones castle because the odd them not logging in to collect nerds is pretty low at the moment.
I don't clear my building until they have been destroyed. I place a brown house farm at the new bit of land, so I should not have any problem having enough available houses for players.
To my friends on here, all 5 or 6 of you :) I would suggest not clicking my castle and attacking the brown house farm on the new land. If you attack my normal, decorated house I may have to clear them due to characters being on tasks.
I have side towns as well, but after I have exhausted those options I attack my neighbors. I start at the front of the list and work my way through. I collect from houses to mark my spot. I eventually will get to all my neighbors.