If you have a basic understanding of markup and styles already, getting them to be compliant to standards is very easy.
On this quest, you will be King Arthur and your knights will be Firefox and its addons. The two main things you should get are the Web Developer Toolbar and Firebug. These will allow you to validate your XHTML/CSS and easily scout out errors.
The good thing about web design/programming is that none of it's real, you can fix what you did wrong in a flash. Even the best designers will have a few errors with compliance but these tools exist to allow everyone to easily find/fix any errors they have. The rules are very simple, you just need to see them once or twice and you'll remember them forever. As long as you have some idea of what you're doing, you'll be OK.