DOORS THAT BIND OR STICK
The first step you should take if a door binds or sticks is to check to see if the hinge screws are loose. Loose screws allow the door to sag and rub against the door frame or the lock's striker plate. Open the door all the way and tighten every screw.
If the screw spins and refuses to tighten, then unscrew it, break a wooden match stick head off, and stick the remaining wood flush into the screw hole. Safely discard the match head.
If you don't find loose screws or the door continues to stick after all screws are tight, then check to see if one or more of the hinges are set too deeply into the door frame.
Find where the door binds by sliding a piece of paper around the edge where the door binds. If it sticks at either top corner, then move the bottom hinge out. You can do this by unscrewing the hinge and slipping a shim behind it. The shim can be cut the size of the hinge back from the thin backing cardboard of a legal pad or something similar. If the door sticks at the bottom corner, then shim behind the upper hinge as described.
You install shims by opening the door to 90 degrees. The door needs to be held up when you loosen a hinge. Prop open the door with a home repair magazine or two underneath it and take the screws off he back of the hinge at the door frame. Allow the door to rest on the magazine(s). Put the shim in and replace the hinge screws. If the door still sticks, try a second cardboard shim on the proper hinge.