Oklahoma City renters are often subject to long leases. This means that leases will be coming up throughout the year however, and are often advertised well before they actually expire. If you start looking three to four months before your need an apartment, you should be able to find an apartment.
Oklahoma is a major metropolitan area. This means that there are several areas of town where landlords are unscrupulous and may look to take advantage of out of town renters moving to the city for the first time. Always do some background research before accepting a place, and never send any money without actually seeing the apartment in person.
With I-35, I-40 and I-44 running by the city, the freeways and a car are one of the best ways to navigate the large city. If that's not an option for you, you can take advantage of the EMBARK system of public transit. Most of the city is serviced by the bus system, and it can work well for someone living in the city without a car.
To get the quintessential tourist experience, head out to Frontier City for cheesy fun, rides and attractions. If you're looking to get a little bit of local flavor, there are museums focusing on the local culture that range from the Cowboy and Western Heritage Museum, to the Banjo Museum. Oklahoma City features some great ethnic restaurants including ample Thai, Greek and Italian selections. There are lots of great bars in town, but the microbreweries are one of your best bets for a great beer and good time. Try the Bricktown Brewery for starters and go from there.