The first thing you will need to do is determine what your site is going to be about. Some ideas of topics are;
Develop your content separately. Really give yourself some time to think about;
After establishing the my topic and possible types of content the site will need, you should start actually creating this content.
For example, if this is going to a personal website, you might need to pull together;
(NOTE: This is likely not an inclusive list.)
Initially, you should pull together all materials, as high-quality, full-size assets. You should only compress and shrink assets once you know the destination format, placement, and sizing.
You will of course need to tweak, alter, or completely change material as you integrate it with your site.
In addition to pulling together your content, you should make initial decisions about a color palette to be used throughout your site, as well as possible font families that you can use for headings/titles, and body text.