If you want to assemble the skateboard yourself, here are some instructions to help you:
Using these guidelines, you should be able to get the perfect board for you. And remember, as you skate, pay attention to what you like and what you don't -- these aren't hard and fast rules, but just good guidelines to start out with. Every person is different, and every person's own skateboard should be different, too. Once you have your own skateboard assembled and ready to go, just slap some stickers on it and hop on! If you are brand new to skateboarding and want to read some simple steps to help out, read Just Starting Out Skateboarding.
If you got lost or confused on any of these steps, you can always write to me (follow the link above), or ask for help at your local skateboarding shop. This article is rather in-depth, but you don't need to know all of this in order to get a good skateboard. Many companies make complete skateboards designed for beginners that are a good choice (read this article to find out more about Beginner Complete Skateboards), and almost every other skateboarding company has complete skateboards that can be ordered.
And as always, remember the most important thing - have fun!