What will it be used for?

This is the first question you need to ask yourself. The answer to it will decide the budget and the components you will use.

If this is your first build, it is more than likely you will be building a fairly standard mid range machine. Something to browse the web and write a few word documents. However you may want something a bit faster that can handle gaming or watching blu-ray films.

Once you know what you want your new computer to do you can start picking the components. This can take a while making sure that they are all compatible with each other but it will be worth it in the long run.