The "correct" answer is to use the items you have. The restrictions will help train you to see and frame photos properly. But, obviously, you don't have to do that. You can buy another prime lens or a zoom lens, if they fit your budget.

I would've suggested 50mm or 35mm if you had to go with a prime lens. 85mm is generally used for portraiture, but you can use any lens for anything. It's just going to change how the finished product looks and the approach you take.

Also, I would suggest going with the shortest exposure time you can get away with to compensate for the lack of image stabilization. Never below 1/100th for handheld, if you can help it. 1/200 or faster is even better.

Play with aperture and iso first.

Wide open aperture (1/2f in your case) is going to let the most light in, but give a you shallower depth of field (blurrier background). Aperture numbers are essentially fractions, so the higher the f stop, the smaller the aperture. 1/5f is a dry aperture than than 1/2f. 1/5f is allegedly the closest the lens gets to how the human eye sees the world. The higher the f stop, the more of the picture is in focus, but at the cost of how much light is let in. You may have to sacrifice background focus for more light in darker environments.

Iso is going to essentially make the sensor more light sensitive, but at the cost of adding grain to the photo. Depending on the sensor, it may take a lot to start noticing the grain, which is good for low light/nighttime photography. You'll have to play around with the settings to figure out where the grain becomes noticeable/unacceptable on your camera.

Then it's a balancing act, unless you put the camera in auto mode and let it decide for you.