To fix the lights correctly first you need to get out the ladder, string them up in pattern that results in the outline of Santa and sleigh. Adjust pattern until it is clear to bystanders that it is not an ameboa, revision of Dali's melting clock.
Spend hours looking for extension cords. Find them under winter horse blankets that need washing (again).
Plug in to discover that there is a short somewhere in house electrical system.
Try to find a different outlet that the extension cord reaches.
Go buy new extension cord.
Return to lights. Pull out all bulbs and rearrange into pattern of red, yellow, green, blue. Discover that pattern results in awkward blue next to red. Re-do.
Sorry couldn't help it! - If the lights are a bit older, check the insulation.
They should have come with spare bulbs and fuses. Whether or not you kept those and can find them is another matter For the single bulb out, replace the bulb. For the portion of a string, I'd try changing the fuse first - they are usually in a little sliding door or such on the side of the plug.
If those two things don't work, I usually just buy a new string. They are cheap enough that I'm not going to waste hours trying to fix them.
In my stoner youth I kept a string of programmable chaser christmas lights around my living for four years. It's all about replacing the burnt out bulb and then if the string is out the fuses. I kept spares around and takes a minute just to slide the little compartment open and pop out the dead fuse and replace it. I have since grown up and no longer have hypnotizing lights around my living room ceiling but I sometimes miss them. They were festive all year round.
Thanks very much. This is what the Interwebz is for: Instant gratification of the most random requests. And! The info is neatly filed in an orderly fashion: Archived on the late-August 2011 COTH OT Day. And some very technical advice from a stoner. Makes sense to me.