Good Working Practices
HTML is not a formal mark-up language and it has very few rules. It doesn't insist that text entities, such has headings, have to specified using (heading) format tags. Some people actually write documents without marking-up a heading by using a heading style whilst others produce whole documents using a header style for the body text! Both are bad working practices.
Design and use a common style for all your HTML documents - they will then look as if they have been written by the same author!
Get into the habit of writing good HTML documents using standard tags. HTML is still developing and recent releases offer a wider varied of text layout formats, for example HTML version 2.0 didn't allow for the centring of text (but HTML versions 3.0 and above does). Remember HTML is only part of the story - its the browsers that uses the mark-up tags to display the text and these might get less forgiving if sloppy HTML mark-ups are used as browser technologies develop.
As your experience grows you will want to experiment with text layout and colour. We are not all trained designers and very often what we think looks good may for some people be unreadable. Making your Web pages assessable to all reader is not obliquity in education it is now law. Further information on Legislation and Web site Design can be found elsewhere in the Web Centre.
Finally, DO NOT make your documents too large - think in hypertext terms!