Get a driver's license, register to vote & live in the state for 12 months prior to school starting. Nevada doesn't have state income tax, so proof of state-taxed income isn't quite the issue it is in other states.
Or, conversely, get a job with the university system. I had a couple friends in the first year class that worked as "groundskeepers" for a couple of weeks prior to school starting, and this granted them residency.
Check UNLV's website. I believe if you can get a job working for a state public institution (ex: UNLV) then you get residency. So, if you have the means, I would suggest trying to get a job at UNLV doing anything, cuz that will save you a pretty penny your first year.