There are tons of material on the web.
CANSPAM - US - opt out
CASL - opt in, explicit and implicit permission required starting July 1, 2014. Do not pre-check any opt in box
EU - not 100% sure, but offer opt out and must require opt in on the form, no pre-check. That should keep away probemsThe cookie law also applies and that is mostly something you need to do. Adam Waterston had a great set of slides somewhere on cookies.
The EU cookie setting in Admin should be checked to comply with the law on your instance.
Your legal counsel will have access to opinions and detail and you should run your procedures by them.