Gmail has the best spam-blocker of any of the mail services I've used.
Use unsubscribe on any emails from some place you have done business with. Otherwise, don't. Just mark it as spam, and after that, gmail will dump it in the spam folder. Check every few days and make sure there isn't some legit email in the spam folder.
When you buy something or look at a site, often there is an option to get "updates and special offers" or some such thing. Unless it's a site where you really want them (and sometimes they are good deals) DO NOT check that box.