Here’s help to cure your sticking doors.
Determine where it sticks by looking at the gap between the door and the jamb. Once you’ve isolated the area, put a sheet of carbon paper between the door and the jamb (carbon toward the door) and shut the door. When you open it, you’ll see black marks where the door is making contact.
Let’s imagine it sticks at the top (just reverse the advice below if the problem’s at the bottom).
Tighten the top hinge screws first. If you find the screw turning easily without tightening, the hole is stripped. Get some long screws (at least 3″) and drive them right through to the stud. If this doesn’t work (in older homes, plaster and lathe can get in the way), you need to plug the hole. Use sawdust or wood slivers and carpenter’s glue (make sure it’s dry before you try screwing, or your screw may never come out). A wooden golf tee also works well. Just drive the tee into the hole, and chisel or power-sand off the tee head.
If the screws are tight and the door still sticks, you have a few options.
If the door looks like it’s hung reasonably square, you may only need to sand the offending area. Sanding off a slight excess is preferable to planing, especially on the exposed latch-side of the door. It’s easier and neater, and you may even be able to do it while the door is still hung.
You might also re-set the top hinge slightly deeper… or shim the bottom hinge, by putting a thin wafer of wood or other material between the hinge and the jamb to straighten the door.