It is really very irritating and frustrating when you find it difficult to open a door. If you have any problem like this get it fixed immediately. Different kinds of doors have different solutions so we solve them in different ways
Conventional doors: We all have such doors in our houses, if that door gives you problem, you must examine it properly by checking the hinges and door knobs. Check the edges of the door if they need to be trimmed? Make sure that the hinge leaf is placed properly in the hinge mortise. Tighten all the pins of the hinge with a screwdriver. Remember that the gap between the door and the frame should be 1/8 inch. Check the door latch and door knob, if they are properly seated in its place. If there is rust in any part you should clean them immediately.
Sliding doors: sliding doors require different treatment but solution can be made in a little time with simple tools. First of all, to keep it from getting immovable, keep it clean. If it gives you problem in opening check the track, remove the dirt with a vacuum cleaner and put some graphite powder to make it run smoothly. Open the door a little and compare the edge with the frame, if they are not parallel, they need to be fixed. Check the metal track on the floor, if the track is damaged, bent or dented, get it adjusted or replaced.
Garage doors: You can not take a risk of leaving a garage door unlocked as you have many valuables there. Before taking out your tool box, examine the door if there is any interference in the door for example any small thing stuck in the door, if not, check all the parts that make up the door mechanism; like the springs rollers and cable. Tighten all the screws, remove the dirt and lubricate the pulleys. If any thing needs replacement then get it done.
Patio doors; if your patio door is giving problem then check the track at the bottom of the door if there is any foreign object, simply remove it. Wipe the door with damp towel and clean the dirt. Sprinkle graphite powder into the rollers and swing the door back and forth so that the powder goes into and round the rollers. Spray oil on the rollers to lubricate them. Apply paraffin wax or grease to the track and move the door back and forth to spread it properly.