Magic

"Any sufficiently advanced technology is indistinguishable from magic." --Arthur C. Clarke

Technology is a wonderful thing. As a person who has spent an average of, oh, ten hours a day on the computer this summer, I feel perfectly justified in saying that. Now, technology can really be anything at all mankind has created, from simple flint arrowheads upwards; but I'm guessing if you're reading this that you're more interested in the "fancy" kind, computers and FTL (faster-than-light) drives and cloning and... So that's what I'm going to talk about. Just remember, technology can be simpler than this; one of the most memorable short stories I ever read, The Road Not Taken by Harry Turtledove , dealt with a group of beings who managed to come to Earth with only stone-age or maybe early bronze-age technology somehow came to Earth...ooh, that's a delicious story. Anyway.

As with many things in world-building, your technology is going to rely heavily on the question "Why?", which is going to rely heavily on your world's history. If your characters are warlike, much of your technology may be related to weaponry and defense. Mercantile societies may have complex financial predictors and models on their computers and/or a completely computerized financial system. Physically weak species could have lots of robots running around, doing what the sentient beings cannot. Highly social cultures may work towards artificial intelligence (or away from it), and so on.

And, again as with many things in world-building, you should make sure your technology is coherent. It doesn't make much sense to have teleportation and slide rules coexisting, for example, unless you have a really good reason for it.

Another aspect of technology to remember is medicine. First, of course, you'll have to know what kinds of diseases and injuries your characters are vulnerable to; then you need to figure out how much they can fix. Invulnerable characters are boring, of course, but it's not too much fun if they can die from a shaving cut, either. Also think about what kinds of devices and materials are needed for cures, and how portable they are. Does everyone need to go to a hospital, or can everything be cured at home? Do you take pills or shots or implants or hear strange ringing noises to help the cure? This information is a lot more necessary for those in dangerous situations than those in comfortable situations, but it's applicable to everyone, more or less.

Finally, you should think about power sources. How do you get the energy to do everything your technology does? There are many answers, some plausible, some highly implausible, but they're all necessary: without magic, you can't make something out of nothing. And if you're going to use something that's at least theoretically possible now (i.e. fusion), please, please, please, I beg of you, do your research. Fusion, even "cold" fusion, has some nice high temperatures to go along with it--and multiple other issues as well. But even if it's something completely crazy, at least know what's providing your fuel. Besides being fascinating to your geeky science-loving readers like myself, it can provide a number of interesting plot points.

	In the movie Galaxy Quest, a large section of (hysterically funny) action takes place when the crew of the spaceship has to go find a new "beryllium sphere." In the course of the search, the crew encounter cannibalistic, childlike blue miners and a rock beast. This plot point was probably a comment on Star Trek, which the movie consistently parodies; see the original series, the Next Generation, or the movie The Wrath of Khan for all the fun things that can be done with a warp drive.

Actually, I think I'm going to end on that note: Do Your Research when you're dealing with technology. It's a generally science-fictional concept, which means it's probably based on what we have now, which means your readers are more likely to have ammunition if you mess something up.

A lot of the rules that apply to magic apply to technology, at least advanced technology, so you might want to check out that essay too.