I've been to the Vegas convention every year since 2002, plus other Star Trek and general Sci-Fi conventions in Vancouver BC, Seattle, Portland, Los Angeles, and Salt Lake City (I think around 45 or so in total since my first one in 1992). Here are my suggestions--
* Talk to people in line around you. I have met people from all over the US and from all parts of the world, including Japan, England, Scotland, Germany, Australia, Chile, Canada, Spain, Peru... A big part of the fun of the convention for me is just talking with other fans, and I see many of them again each year. If you have business cards, or just make some up on your home computer, it makes it easy to trade email addresses.
* Bring some snacks. There is food available in a sandwich/salad kiosk just outside where the convention is held (inside the Hilton convention area), but it can be kind of pricey. Farther away near where the Experience USED to be there is a Pizza Hut, and there is a nice buffet at the Hilton as well, but if you throw a few granola bars or whatever you like to munch on into a backpack, you can save money for things from the dealer's room The Hilton provides large jugs of ice water and plastic cups in the actual convention hall, in the dealer's room, and outside the convention hall, so you don't have to worry about bringing bottled water unless you really want to.
* Bring extra batteries and memory cards (or film) for your camera. Besides getting shots of the stars while they are on stage, you'll see a lot of folks in some cool costumes. Most of them don't mind at all if you take a photo with them.
* Dress up if you can-- it just adds to the experience. I'd say that at the Las Vegas convention, about 20% of the attendees wear a costume of some sort, or at least a uniform top with jeans. About another 20% wear a Star Trek t-shirt or baseball cap with regular casual clothes, and then the rest are mostly in shorts, jeans, and T-shirts. I like to bring a different costume for every day and really go all out. In the past, I've dressed like a Klingon, an Andorian, Mr. Data, and a Borg. This year, there will be an attempt to break the Guinness Book of World Records for most Star Trek fans in costume gathered together.
* Despite being in Las Vegas in August, the actual convention hall tends to be on the chilly side because of the air conditioning. If you get cold easily, you might want to bring a sweater or a long-sleeve shirt.
* The Dealer's Room is large and has a nice variety of things, from actual screen-used costumes and props (these can get pricey) to models, toys, patches, fan-made uniforms, action figures, videos, books, art, t-shirts, 8X10 photos, posters, CDs, etc., and not all from just Star Trek. There is merchandise from Star Wars, the X-Files, Battlestar Galactica, etc. Most of the vendors are equiped to take credit cards, but having cash on hand doesn't hurt.
* I am not really into autographs or photo ops, but the lines for really popular stars can be REALLY long (sometimes over an hour). Photo ops and autoraphs can sell out quickly, so if there is someone you would really like to get, buy your ticket for them sooner rather than later.
* There are other supporting actors in the dealer's room, and generally you just walk up to their table if you would like a photo or an autograph. The Creation website has the price list for each person appearing.
If you have other questions, let me know :-)