Size Does Matter

This axiom applies to virtually every aspect of designing your website.  Keep your HTML coding clean; it reduces the risk of errors and helps the page load faster. 

Use external Cascading Style Sheets; this also helps the page loading speed and makes it easier to make website-wide changes with updates to a single file.

Picture file size should never be larger than 100KB; consider also using thumbnails if you wish to include sharper detail to display your product.

The largest picture display size should be 500px by 500px or smaller, unless you're linking from a thumbnail to a full-size -- the full-size should be 800px by 800px or smaller.

When working with frames, do your best to avoid scrolling in the navigation and/or header areas.  The scroll bars detract and annoy the average viewer.

Be aware of the size of the background and logo you choose.  While most backgrounds and logos are not a problem, there are some that require horizontal scrolling which can be an annoyance.