While Vegas is a place to spend cash, and typically the more you spend the more fun you can have, you don't have to go for broke to have a good time.
My few tips:
Prices can be hyper inflated in places, especially nightclubs. Accept this and don't get pissy.
I'm not in the camp of getting a table at a nightclub - I'd much rather be in the thick of it on the floor from open to close, going hard and shit. Lot's of slimeballs treating it like a meat market, but usually there are plenty of people there simply having a good bloody time. I think the last time I went to Omnia I only got one drink? So something like $60 total for almost 7 hours of damn good fun.
If you do plan to head out, plan a tiny bit and get entry in advance and avoid the bulk of lines. I don't really understand the allure of standing in line for hours to save a few bucks.
Even though you're under 25, rent a car. So many sweet places within and around Vegas to check out. Most hotels still have free parking. It'll be hot in June, however. Avoid driving the strip at night unless you like not moving.
With said car, get booze at places like Lee's. Stash up and get sauced up before going out if that's your thing.
Poker is super fun, but there are local grinders looking to cash in on tourists. Bellagio poker room is my favorite. Good action, feng shui and the drinks come frequently. Despite their reputations, not a fan of the Wynn or Venetian rooms (the latter in particular). Learn the basics of craps (you can do this at a casino for free), find a low min table, and have a bloody good time (assuming things go well...)
Stay middle strip. It's tempting to stay further away to save cash, but to hell with that. High season weekends can be horrendously expensive for what you get, though.
In that same thought, check out options like Airbnb. I did for next month at city center, and not only do I get to avoid the weak-as-hell "resort fees" but I get a full kitchen and a fridge I can actually use for my personal effects. Saved tons of money and got a better room overall. Great for a group of people.
Groupon/living social are perfect for Vegas, so check those out for random fun things you can do. Never know what might pique your interest.
Good food options everywhere, both on the strip, downtown, and elsewhere in the vicinity. With a car, you can hit up some realllly good places off strip. Check out http://vegas.eater.com/
for an idea of some options.