Obviously how long you're going to be in town will affect your plans since you may have to eliminate some good stuff to be able to get all the really good stuff on your schedule. How long it's been since your last trip to Vegas also makes a difference because you'll want to focus on the sights that you haven't seen instead of going back to the things you already have.
And finally your budget is important because that will help steer you in one direction or another. If you don't have a lot of money to blow, you can still fill up your time with the free or low-cost attractions and shows. If you're not much of a gambler, you can spend the money that most people pump into the slot machines on one of the big-ticket productions.
On Vegas4Visitors.com and other websites like it you'll be able to find information on all of the things you can see and do while you're in Vegas. Go through the Attractions section, the Shows section, the Nightlife section, the Shopping section, and the Recreation section and make a little list of the items that sound appealing to you. Maybe you want to see all the big shows or maybe you're a thrill junkie and have to hit all the roller coasters and rides. Perhaps you're an animal lover or a shop-a-holic. Whatever your taste, you're sure to find a lot to suit it.
But my recommendation is to be well-rounded in your Vegas trip. If you have the time and budget, try a little bit of everything - maybe a trip to see the Dolphin Habitat in the morning followed by a roller coaster and a museum in the afternoon with a show and a trip up the Eiffel Tower Experience at night. Don't book yourself up with a lot of the same types of activities - and be sure not to overdo it - you're on vacation after all!
Once you have your list of sights that sound interesting, rank them in order from the "sights you absolutely cannot miss" to the "sights you'll get to if you have time." Then apply your budget to eliminate the ones you can't afford, working up from the bottom. Next, apply your time constraints, getting rid of the places you just won't have the room for in your schedule.
That will leave you with a sure fire list of things you want to see and do, and hopefully a picture perfect Vegas experience.
Next: Managing Your Money