One of the mistakes I frequently see in "professional" websites is a lack of consistency across the entire website. Different pages might be laid out slightly different, or they might have different background images. In extreme cases, I can't even tell if I'm on the same website, aside from looking at the actual address of the site.

This lack of consistency across the site shows a lack of professionalism. Even if all your other business material is extremely professional, a website with that problem can bring your whole business down. Potential clients who look at it will have a lesser opinion of your business as a whole.

There are several things that should be the same across all of your site.

• Layout - The menu should be in the same place on every page, as should things like the header and the main text of the page.
• Background - This includes color and/or image.
• Menu - The actual order of the menu should be the same on every page.
• Colors - Links and text should be the same colors. That is, if all your menu links are white, the menu links on every page should be white. If all your main text links are blue even though your menu links are white, that's fine, but each page should be the same.
• Header Image - This should be exactly the same on every page.
• Width - You should not set one page on your site up to be 760 pixels wide, and another 100% wide. They should all be the same.