two threads:

http://www.flopturnriver.com/pokerfo...ad-177296.html
http://www.flopturnriver.com/pokerfo...ge-177508.html

and a special hint for after you read those threads and put your opponent on a range:

if you beat more than 50% of what you think your opponents CALLING range is on the river against your chosen betsize. then that is a bet which has a positive expectation. they're the good type.