Best Practice in Web Design...
Designing for the web restricts your font choices. If you specify a font that a user does not have, their browser will substitute a default font, changing the look of the page.
Choice of Fonts
The web page will look clearer if you choose fewer fonts and type sizes.
Decide on a font for each different level of topic importance. For example you should have a different font for page headings, section headings and body text. Effective use of different fonts for different levels of importance will guide the user through the content more efficiently.
Choose different size fonts of the same type throughout the site. Consistency will help you to develop a strong visual identity for your site.
Availability of Fonts
The user's browser and operating system determine how a font will be displayed, so you can't be absolutely sure how your page will look. In addition, if the font is not available, then the user's system will default to a standard font.
Remember to use commonly available fonts and test your web pages on multiple platforms to see what effect these have on the overall appearance.
Ensure the page is Legible
The size and face of the type used on the page determines the legibility of the text. Remember that it's harder to read on screen than from a paper copy, so keep fonts big enough to be comfortably read online.
To make things easier for the user you can add more white space around the blocks of text and between lines, both of which will help with clarity.
Make sure that you have enough contrast between your text colour and the background colour. Dark backgrounds frequently make the text difficult to read, so opt where possible for darker text on a lighter background.