Determine whether the rim is bent ("out of true") or not (true). A bent rim can cause the wheel to rub against the frame or brakes, impeding smooth rotation. Possible causes of a bent rim are improper transport and hard, off-center impacts while riding. If your rim is only slightly bent, it can be trued.
Use a spoke tool to tighten spokes near the bend, creating tension that will force bend out of the rim.
If in doubt, refer to a bicycle repair manual or take the wheel to a bike shop to avoid overtruing or damaging spoke nipples. A badly bent rim should be replaced.
The brakes might be seized shut, prohibiting the wheel from rotating. Look over the brakes to ensure there is ample room for the wheel to rotate between them.
Check that the brake lines are not caught on anything that would cause tension on them even when you are not squeezing the brake lever.
Refer to brake maintenance specific to your style of brake or consult a bike shop if you discover a problem.
Remove the wheel from the dropouts, which might require a spanner. Most wheels build in recent years can be removed by hand.
Insure the hub is not damaged. If the hub is damaged, it should be repaired or replaced by a bike mechanic.
Reset the wheel. Be sure the axle is sitting firmly in the dropouts. If the axle is askew, it will prohibit smooth rotation.