How would be the best way to get bats out of attics?

Try this site.
http://pestcontrol.netfirms.com/bat_control_without_poison_bait1.htm

Take a flashbomb or a stunbomb that you can win/buy from the statefare

The best way is mechanical exclusion. Find their entry point, normally a gable vent, and cover the exterior with plastic sheeting. Leave the bottom open but flush with the house so that they can leave but not return. After 3-5 days put screening over the vent both inside and out to keep them out next year.