Paint Your Door
Remove the door from the doorjamb, and take the hinges and doorknob off of it. This will enable you to give it a thorough paint job without getting any paint on the hardware.
Scrape any loose paint off. Paint that is still secured to the door should be scuffed up with sandpaper until the sheen has been removed, in order to increase the adhesiveness of the new coat of paint.
Prime any surfaces that you have stripped down to bare wood.
Apply a finish coat to both faces and the edges. For added coverage and protection, apply two or three very thin finish coats.
Refinish Your Door
Using a scraper, a putty knife, and some 80-grit sandpaper, remove paint from the faces, edges and trim of the door. For difficult paint on profiled trim, it may be worthwhile to grind a piece of metal into the shape of the trim and use it to scrape paint out of the hard-to-reach places.
Using progressively finer grits of sandpaper (80, 100, 150 grit), sand over the surfaces that you scraped until you have a smooth and blemish-free surface.
Apply several thin coats of clear polyurethane to both faces and all edges of the door using a rag for wipe-on polyurethane or a fine brush for conventional polyurethane. For a darker finish, apply wood stain prior to the polyurethane. Allow each coat to dry thoroughly before applying the next one.
Plane Down Your Door
Plane down the edges of the door if it is sticking. Close it as much as possible, with the face of the door against the jamb. Draw a pencil line down the face of the door, following the line of the jamb and leaving about 1/8 inch between the door jamb and the line.
Remove the door from the door jamb and set it up on sawhorses so that the edge you want to plane is on the top.
Using a sharp hand plane, plane the edge of the door down until you have removed all of the wood on the outside of the line you drew.
Remount the door and test it for fit. If it is still too large, remove it and plane a bit more off.