As well as the other advice, use CSS for determining background colour and so on - it's much easier to change later if necessary. Also consider downloading and installing a web server onto your PC, so you can make sure it works properly that way. There are web sites around that attempt to load images from a local path - something like 'C
images\myimage.jpg' which of course doesn't work for other people. Another common problem is that if the place you upload it to is running Linux, then file names are case-sensitive so MyPage isn't the same as mypage.
Finally, make sure your pages meet the HTML & CSS validation at:
http://validator.w3.org/
http://jigsaw.w3.org/css-validator/
These are not perfect, but will pick up a lot of common problems.