Keep the font color black in a white background. Any other color combination can be painful for the reader’s eyes and challenge those who are color blind. If you still wish to have colored fonts, choose a dark font in a light background with sufficient contrast and ask some of your friends for opinion. Do not use blue color for font as it may be confused with a link. Do not write the post using multiple colored fonts. If you want to highlight a point, use quotes, bold, italic formats.
Use Bold, Italic styles only when needed and not very often. Do not underline unless it is a link.
Do not fill your blog with too many gadgets, scripts. Your readers may not die if you remove some but it will help load the page faster for them. If an external site serving script for your blog goes down, it will cripple your blog too. So keep only the most important scripts.
Browser, OS, Resolution compatibility
Check your site in popular browsers and operating systems and in all screen resolutions. Your check list should have Firefox, Safari, Linux for sure. Your main post content should be completely visible in 800×600 screen resolution.