Go to the clubs that you want to attend during the day. Knock on the door and ask if there are any VIP passes being handed out for the night. This usually works better if you're a female; if you're a guy, send a woman to ask. Usually the bouncer or club manager will have passes available.
Talk to your hotel management, especially if you're in a hotel with a club you're interested in. Ask a manager how to get passes to the club and be sure to mention that you're staying in that hotel. It also helps if you're a member of the hotel's rewards program.
Find the people on the Las Vegas Strip that hand out passes. These people can be found everywhere, but are usually concentrated in the center of the Strip. They will give you passes to any club on the Strip for free, but they'll ask you to tip them for their services.
Talk your way in. This is a last resort, but works really well if you're a female with a group of females. If you're a male, chances are your female friends will get in and you'll have to wait in line.
