It depends on your interests, since there are lots of different things to do in Vegas. My Vegas trips are usually 1-2 week in length, so I tend to do a variety of things like seeing shows/concerts, gamble, visiting the different hotel/casinos on the strip, visit Fremont St. and Container Park, dine out at different restaurants, etc. I often arrange dinner and/or dinner/show dates with some providers too.
There are plenty of other attractions like Stripclubs, the Neon Museum, Mob Museum, Atomic Testing Museum, Pinball Hall Of Fame, Erotic Heritage Museum, Ziplines on Fremont St and at the Rio, etc.
If you rent a car, you could take side-trips to Red Rock Canyon, Valley Of Fire, Mt. Charleston, Hoover Dam, visit some of the off-strip properties like Red Rock Casino, M Resort, South Point, Green Valley Ranch, etc.