Dream incubation is a practiced technique of learning to "plant a seed" in the mind, in order for a specific dream topic to occur, either for recreation or to attempt to solve a problem. For example, a person might go to bed repeating to themselves that they will dream about a presentation they have coming up, or a vacation they recently took. While somewhat similar to lucid dreaming, dream incubation is simply focusing attention on a specific issue when going to sleep.
A 2010 article in Scientific American quotes a few of the incubations techniques from The Committee of Sleep as follows:
If you want to problem-solve in a dream, you should first of all think of the problem before bed, and if it lends itself to an image, hold it in your mind and let it be the last thing in your mind before falling asleep. For extra credit, assemble something on your bedside table that makes an image of the problem. If it's a personal problem, it might be the person you have the conflict with. If you're an artist, it might be a blank canvas. If you're a scientist, the device you're working on that's half assembled or a mathematical proof you've been writing through versions of.
Equally important, don't jump out of bed when you wake up—almost half of dream content is lost if you get distracted. Lie there, don't do anything else. If you don't recall a dream immediately, see if you feel a particular emotion—the whole dream would come flooding back.
If you're just trying to dream about an issue or you want to dream of a person who's deceased or you haven't seen in a long time, you'd use very similar bedtime incubation suggestions as you would for problem solving: a concise verbal statement of what you want to dream about or a visual image of it to look at. Very often it's a person someone wants to dream of, and just a simple photo is an ideal trigger. If you used to have flying dreams and you haven't had one in a long time and you miss them, find a photo of a human flying.
See also: http://en.wikipedia.org/wiki/Dream_incubation
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)