An excellent article based on direct observation by Mary Theofanos and Janice Redish gives some great suggestions on how to improve accessibility.  Here is a partial summary of some of their ideas and a few of my own:

• Write for the web. Screen readers begin reading at the begining of a section.  Those who use them scan web pages auditorily like sighten users scan with their eyes.  Place keywords at the begining of a line of text so they your users have the most important information first.
• Build a page with proper XHTML structure. The wonderful thing about semantic coding is that it makes sense in a hierarchy and provides structural context.  Even though your page may display differently, your markup should reflect what is most important to your user.
• Use proper CSS techniques. CSS is allows designers the freedom to display a page the way they’d like it seen, but is also allows a user the same luxury.  By employing CSS best-practices, you can maximize a users experience by letting them “see” a page that makes sense for them.
• Use alternative text for all images. It always suprises me how many websites still don’t include alt text for images.  Crafting a perfect description for a complicated graphic may be a little tricky, but something is better than nothing.  If an image is purely decorative, it’s better to have an empty alt tag (i.e. alt=” “) so that the screen reader will ignore it.  Having appropriate alt text will improve your search engine ranking for images, which is reason enough to include it.
• Make content, especially forms, keyboard accessible. Tabbing through form fields is something a lot of people do. If you’ve ever watched a computer power user, they often don’t even touch their mouse, or they have one hand on the keyboard at all times.  Some people can’t use a mouse, so this one is very important.

As your tools to create web pages become more sophisticated, you’ll find that accessibility will be a more integrated part of your workflow.  Being aware of the big ticket items will help you move forward in your goal to create amazing work for a global audience.