Great choice and a great start. The 5100 is more than capable of doing a lot more once you know your way around a D-SLR. You'd be surprised how little of a difference there is between these and the Full-frame $10K counterparts for normal use. Your next investment should be either a AF-S NIKKOR 50mm f/1.8G or a Speedlight flash. If you take a lot of indoor shots, the flash is going to be a godsend and will make your images a 1000 times better.
A few easy tips without spending a dime:
-use anything you can that will steady the camera (a tripod would be best) or make sure the room/area is well lit. The kit lens it comes with isn't "fast" since your aperture is probably limited to f/3.5 at 18mm and goes all the way down to f/5.6 at 55mm. This means the camera has to either slow down the shutter speed (longer exposure....more blurry cause by movement or vibration) or increase the ISO (more sensitive...but more noise in the images). By having the camera as still as possible, you'll get sharper pictures without having to spend money on expensive lenses.
-IMO, the best setting to use if you're just starting out but want to be creative is "A" aperture priority and let the camera meter the shutter speed. Then just use the exposure compensation button (it's that +/- square button) to make it lighter or darker.
***Basic rule of thumb for aperture (simplified):
---Smaller aperture
number means a bigger aperture
opening and a larger
number means smaller aperture
opening. You either let more light or less light enter the camera.
---Larger aperture has less stuff in focus and creates that blurred background look (low numbered f-stop), Smaller aperture (higher numbered f-stop) will have the opposite effect and will have more of the scene in focus. A drawback to smaller apertures (higher f-stop number) is that it lets in less light...so the camera has to leave the shutter open for a longer duration or increase the ISO.
-For portraits, always shoot at above 50mm or higher to avoid unflatering destortion....especially women. You just need to stand farther back. They also look best in "portrait" since it doesn't distract you from the main subject of the image. You've got a gorgeous girl, no one needs to see the Mountain Dew on the table
This:
vs. This:
You may know some of this stuff already, but I figured it might help others.