When you become the mayor of a place on Foursquare, you not only get a snazzy title, but you might also receive special treatment or score awesome deals! Mayorships are based on the most *days* with check-ins in the past 60 days (you could have more check-ins overall but fewer check-ins over the past 60 days). Only one check-in per day will count. Keep in mind that you might find yourself neck and neck with another user who is checking in to the venue often, in which case that's all part of the fun!
In order to be eligible, go to your Privacy Settings at https://foursquare.com/settings/privacy and check the "Let me earn mayorships (I realize that mayorship is a public office" box. You also need a profile photo! You can upload a photo to your account in the app or at http://foursquare.com/settings. Note: photos must be 200 KB or smaller (jpg, gif, or png format).
Make sure you aren't checking in privately. Private check-ins do not count towards the Mayorship tally and will not unlock a Mayorship. When you check in, make sure the lock image is gray and not highlighted. And remember, only users who have legit check-ins (no rapid-fire check-ins, no drive-by check-ins, and no fake check-ins) will be able to reign.
Oh, and if you’re using the mobile website at m.foursquare.com, your check-ins will not count towards the Mayor tally. Sorry about that! Details here.
Venue managers and Staff: you are not eligible to earn the mayorship at your place of business (unless it is a home or office). If you suspect that the mayor of your place is not following the Foursquare House Rules, you can revoke the title via the place page, or reach out to @4sqSupport for help.