The most important tag on a page is your title tag, followed after by the h1 and h2 (not sure on h3, h4 etc.). If you look at a well presented site you ll see that either the site title is in a h1 on every page, and the page title is in a h2, or the page title is in a h1 on each page. A standard WordPress site has the site title in a h1 and the post titles are in h2s.