Web authors do not need to change their design approach or methodology in order to produce Web pages that are WCA compliant. In fact, most existing pages can easily be made fully accessible with very little effort or change. Cascading Style Sheets (CSS) are now used extensively for page layout, thereby separating content from presentation. However, pages should function as intended when Style Sheets are turned off or not usable as is often the case with old Browsers.

Easy things that Web Authors can do to enhance the Accessibility of their pages:

Provide descriptive text for reference images, (meaningful description of what the image is and its purpose via the ALT attribute).
Structure pages utilizing header markup., (use h1-h6 for section headings).
Provide a Site Map or List of internal page links.
Ensure links make sense out of context, (natural language text descriptions - avoid "Click Here" or text within images).
Avoid duplication of Link text, (for different anchors on the same page).
Insure that there is good contrast between text and background colors.
Use text that is large enough to be easily read by people with diminished vision.
Do not rely on color alone to convey meaning.
Employ punctuation that is compatible with screen reader usage.
Use proportional, rather than absolute, sizing and dimensions, (% and em rather than pixels).
Design to standards, (for interoperability, ease of maintenance, etc.).

Not providing meaningful alternative text for images is the most frequent Accessibility error committed by Web Authors, fortunately one that is easily corrected. Appropriate Use of Alternative Text by WebAIM is an excellent reference and guide for complying with this essential WCA requirement.