<p>Although I'm specifically interested in web application information, I would also be somewhat curious about desktop application development as well. This question is driven by my work on my personal website as well as my job, where I have developed a few features, but left it to others to integrate into the look and feel of the site.</p>

<p>Are there any guides or rules of thumb for things like color schemes, layouts, formatting, etc? I want to ensure readability and clarity for visitors, but not be bland and dull at the same time.</p>

<p>As for my knowledge in this area - If you hand me a picture, I have enough knowledge to reproduce it on the screen, but if you ask me to design a new interface or redesign an existing one, I wouldn't know where to begin.</p>

Usually, each operating System has user Interface Guidelines. For Windows, have a
look here
. (Edit: The links in that post are broken. But a Search for "
User Interface Guidelines
" on MSDN has articles about everything)
Apple has it's own as well. Also, you may want to keep
accessibility
in mind.