There's been a lot of good advice given already on this topic -- but let me
add a few things I've found useful:
Lead lines aft, and install a jib downhaul. The downhaul made all the
difference in the world to me for singlehanding. It was a trivial
modification to make - search the archives for ideas, or if you're near
Seattle, I'll show you mine.
Learn to heave-to... I use this maneuver frequently when singlehanding.
Sometimes you just need to go below decks to use the head, grab something,
etc, and heaving to is easier and keeps the boat steadier than dropping
sails.
Sail slugs make getting the main up and down a lot easier. Spray 'em with
some silicone spray to make 'em glide smoothly.
Know when to throw in the towel and use the motor. I recommend it for things
like trying to pull into a slip, even when I have crew with me. I often
practice pulling into docks and slips under sail power, but unless its a
situation where I can easily abort (e.g. approaching the lee side of a
dock), I often have the motor idling in neutral ready to save my butt :)
While it is a great show of seamanship to do these things under sail, it is
completely negated by how embarrassed you are if you fail :)