Legibility

Keeping to the most basic and common fonts may not seem very exciting, but by using them you’ll ensure that your design is easily read by your audience. Drop shadows on text, often used to give words the appearance of depth, can be difficult to read. Use consistent typefaces and fonts throughout your site by applying style sheets, pre-setting formatting in body text, header, bullet and title applications.
Size

Upto 12 pixels are recommended font sizes for body text in extreme cases 14px. For Headings its should be maximum 18px. Do not assume that all users know how to change their view or text size within their browser.
At the same time, for those users that may make these browsers adjustments, you need to insure your size changes consistently, or you will force them to make adjustments from page to page.
Typefaces.

The recommended fonts for body text are Tahoma, Arial, Georgia and Verdana. And for the headings Trebuchet MS. Avoid Cursive or handwriting fonts in a professional website.
Type weight

The thickness or weight of the typeface. Many typefaces are available in family sets: light, bold, italic, condensed and extra bold. While boldfaced text appears larger, readability may decrease. Limiting the use of bold to emphasize a title or a key word is recommended.

Kerning/Character’s Spacing

Kerning refers to the adjustment of space between letters in a word. Depending on the design a designer can give tight, regular or loose letter spacing throughout a design or style sheet. Limited or specific adjustments should be done between letters of page title or subtitle text only to enhance designing. Make sure there won’t be any amendments or modifications with character spacing of body text.

Advice: Try to use more decent font rather than modifying Character’s Spacing values.
Line Height

Avoid line-height in paragraphs and if there is need to give line height it should not be more than 16px. However, for vertical menus u may use line height acc to the design, may vary between 20-28px.