Doors are always a pain in the ass to deal with.  Let’s go over some common problems.

Squeaking

Quit using that crappy WD-40 on the hinges and use something that actually has the word “oil” on the can.  Blast the hinges with the door both open and shut, paper towel at the ready to wipe up the spillage, and then open and close it a number of times.

Sticking

There are a few things you can try if it’s just barely sticking, but otherwise the standard routine is to sand down the edge of the door with a belt sander, and make sure to take off some extra for both the coat of paint and future sag.

If it’s just barely touching, grab a small piece of 2×4 and a sledgehammer, hold the 2×4 against the edge of the door where it’s sticking and slam it a good one with the hammer.  You’re not trying to ‘bend’ anything so much as ‘resettle’ things.  Then give the hinge screws a good tighten.  This may work for a while, but the problem will probably come back.

If that doesn’t work, take the hinge off the wall opposite the sticking and chisel it out a tad.  You can only take out a sliver, and the door might bind a tiny bit in the last few inches of closing, but it’ll get rid of the sticking.

If it’s hitting too much for either of the above to work, it’s time to do the saw & paint routine.

If you just want to live with it, call around to the local old-type hardware stores and dig up one who sells beeswax, or dig up a small can on the Web.  Everything else (Vaseline, soap, wax, etc) rubs off too quickly.

If the problem is the bottom of the door hitting the threshold, count yer blessings.  At least you can saw or sand it and not have to bother repainting anything, although you should hit it with a coat of water sealant.

Locksets

A fairly common problem is the plunger or deadbolt hitting the strike plate because the door’s settled a tad. Usually it’ll just be missing by a fraction of an inch, so attacking it with a metal file is the way to go.  Clamp the strike plate in a vice if you have one (Vice-Grips otherwise), then start filing away.  The metal’s fairly soft and won’t take much.  You might first dig with the edge of a square file, then finish off the rough edges with a round file.  Take off a little extra for future sag.

If it’s really bad, you’ll want to remove the strike plate, re-chisel a new setting for it, then drill new holes for the screws.

Gates

This is usually a case of sag.  If it’s just rubbing a bit, a belt sander might be the answer.  If it’s worse than that, you’ll have to re-mount the hinges.  Unlike doors, however, which have recessed hinges, gate hinges are usually easy to deal with.

If that can’t be done, and there’s something solid nearby, like the house, you could consider running a steel cable to the gate post with a turnbuckle to pull the post back to its original position.  You could use a wood or steel rod, but the turnbuckle will allow for future sag to be easily corrected.

When it comes to boards falling off, use ribbed nails or those wide-threaded ‘contractor’s screws’ and a drill gun with a Phillips head attachment.  Regular smooth nails should have been banned from existence the day ribbed nails were invented.