What are the most important things to consider when building a website?
First of all you have to decide what kind of website you want. Do you want a sub-domain under a top level host or do you want your own site? If you are just starting out I would recommend a sub-domain under a top level host.
Why, because it is the cheaper way to go. You can always forward a site you own to it later or move it entirely to your own site.
Second you have to decide how you are going to build the site. There are a number of good alternatives out there such as WordPress that are easy to use. I remember when you had to code each page in HTML. That was a little bit like programing. Luckily it is not that difficult anymore!
After that I usually map out the structure of my site. I usually think of it like a flow chart. Start with the home page and then write down the individual pages you want. Sometimes you can get away with a one page site depending on what you are using it for. I usually like to have three to five pages on my home page menu. You do not want too many because it makes it difficult to see all the choices. Sometimes if I have more pages I make them accessible from the other pages, but always keep a link back to my home page.
Unless you are doing a blog only site do not forget about graphics. People like to see pictures, even on blogs to be honest. Just make sure they are relevant to what you are promoting or talking about.