I never really get any... I've been using gmail for about two or three years and I've had a total of about 3 or 4 spam emails... When I do get them I use the gmail "report as spam" button, then the unsubscribe button, then delete it, and try to figure out how they got my address in the first place.
Gmail lets you do something neat, any "."s you put in your address are ignored, so I can put email@example.com or firstname.lastname@example.org or whatever, depending on who I'm giving it to... If I find that I'm getting spam at email@example.com I can filter it so they all get routed to my spam folder.
That's how I found out it was my bank who was spamming me, so I filed a complaint with the better business bureau and canceled my account with them.