Using fonts
It is easy to get carried away when you are setting a web page.
You want to emphasis this and that, and then before you know it the text on the page is getting larger and larger.
Hundreds of years of typesetting have established a rule of thumb "never use more than 3 font sizes on a page", because you are basically firing too much information at a reader - like 3 people talking to them at once.
Next time you are setting a page try typing the whole page in p first. When the content is composed, go back and highlight headings and sentences adding H2 or maybe H3/4/5/6 as appropriate. Use H1 size as the heading only.
It is very important that you only use H1 on the page once at the top because the search engines (Google, Yahoo! and MSN) may ignore anything but the first six words when indexing your page - which might be the difference between someone finding your website and not.
Don't forget to set your zoom level to 100% because that is how most other people will see your page. Zoom is on the View menu of your browser.
When setting the design for your page, take a few minutes to search for similar pages (try to limit your viewing to professionally set out websites) and try and emulate some of the design elements. The BBC win awards for their website design - have a look at some of their pages dedicated to television programmes, including the children's pages, and study the sizes of font, use of white space and sizes of images. This research will help you build a great looking page too.
Websites of interest
http://www.bbc.co.uk/expeditions/amazonarachnids/stories/worldsbiggestspider
http://news.bbc.co.uk/sport1/hi/football/teams/f/fulham/default.stm
http://www.bbc.co.uk/doctorwho/s4/features/interviews/interview_oli_smith_01
