We get several questions about mnemonics, so we'll put up a small explanation for you.

Mnemonics is a memory aid, and they usually serve an educational purpose. If you want to remember the names and order of the planets in the solar system, you could go like this:

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.
My Very Easy Method-Just Set Up Nine Planets (The first letter of each word gives you the first letter of the old list of planets, in order)

They can be useful in the short therm, but unfortunately the technique is hopelessly old and inefficent. Mnemonics are quite popular in some professions and most medicine students have been using mnemonics troughout their education.  They have been around for ages, and were first described in Cicero's De Oratore. Mnemonics are most often verbal, a list of words that are easy to memorize or a short poem. Associations between these easy to remember words will help you to remember your list because the human mind more easily remembers data attached to personal, spatial or otherwise meaningful information rather than information in a meaningless order.

With the new techniques availible today, they can not be seen as a very efficent way of memorizing. Check this free manual for far better and more advanced methods than mnemonics.