1. DOCTYPES are essential for browsers to know how to render your page, especially older browsers. The three main types are Strict, Transitional, and Frameset.  Strict is probably the best choice unless you plan to use deprecated tags.  There’s no reason to re-type this code every time you create a page and increase the chances of getting it wrong.  Copy the code from an authoritative page, or let your code editor to do it for you.  I’ve set Dreamweaver to render the strict type by default.
2. XHTML is flexible but it requires your code to be written correctly, which is a good thing. If you can validate your code, it’s more likely to display the way you want it to.  All tags need to close.  For example: <p>A sample paragraph with a couple of sentences… must end with this tag </p>.  Tags that don’t have an enclosing tag, still need to close.  These are called empty elements, and the image tag is an example: <img src=”dog.jpg” alt=”My Dog Skip” />
3. All tags should be written with lowercase characters. This one is easy to implement.
4. Correctly nest your elements. Certain tags are block level elements and others are inline.  The div tag (which stands for division) is a block-level element.  If you assign a background color to a div and put some content in there, the div will look like a box.  Links (or anchor tags) are inline.  You can wrap an anchor tag around a word in a paragraph, and it will stay “inline” with the rest of the text.  I have been tempted on occasion to wrap a link around a div, which is a no-no.  You shouldn’t nest block-level elements in inline tags.
5. Use encoded equivalents for “&” and other special characters. You’ve probably noticed a funny character when looking at some web pages and wondered what it is: ?.  It’s a white diamond in a black question mark and is called the Unicode Replacement Glyph.  To insure that all ampersands, quotation marks, dashes, etc. display properly, use their encoded equivalents.  If your authoring software doesn’t suggest a code, check out this reference.

I don’t consider this an exhastive list on how to write proper XHTML because there are many ways to mess it up.  It does include some of the most important ideas and the most common errors.  Now go and fix all those pages you’ve made that have problems!

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.