From PSD of or other graphic source, is usually just make a folder and start work. Create a git repo (bitbucket or github). Use local webserver (WAMP or MAMP) to test.

ID the repeated sections, build those in order (header before footer). Haven't ever used a sitemap. Figure out the page archetypes depending on the project type. Article site has frontpage, category list, article page. Ecommerce add product page, checkout pages, user account page etc.

After the basic pages, figure out what additional patterns are to be supported for general page types. Articles have to support Lists (ul/ol), tables, images ... . Then any specialty items like pricing tables.

Write those out as partials so they can be included in different pages if necessary for testing.

If it's a personal project or not already laid out, it's do some basic mockups and then go through the above process. Course there's more involved in this type of deal since have to determine structure for the site based on the site objective.