1. There is NO Substitute for Basic Design Sense
All the formal training in the world (color theory, typology, object distribution) cannot compensate for a basic failure to be able to perceive what looks good and what doesn't.
2. Don't expose yourself (a lesson from Proverbs 17:28).
Proverbs tells us, "Even a fool, when he keeps silent, is considered wise". Such is true in design. If you can't pull off the jaw-dropping great effect, keep it simple and maybe no one will know.
3. Be Consistent Throughout Your Site
Every page should match the overall look and feel of all the others, and don't forget about your "Missing Page" file (404), search results, or script results.
4. A Strong Logo is Invaluable
5. Color Should Reflect Content
Most clients will already have some sort of color scheme. If not, the nature of their product or services should give you a place to start.
6. Be VERY Careful with Background Images
With rare exceptions, solid color backgrounds are the way to go.
7. Use Pictures Whenever Possible
People love pictures of other people.
8. Look at What Others are Doing
Find inspiration in the successful sites of others in the field or others who are trying to appeal to the same demographic. Don't be afraid to "View Source".
1. Use Style Sheets to Control Your Fonts
Big, unruly, "times-like" font are a major tell-tale sign of amateurism.
2. Use Tables (but keep them hidden)!!!
You need tables everywhere to ensure that your text and images don't wonder. Without them, there's no telling how things will line up.
3. Design with Components (or whatever they're called in your HTML editor)
All common elements should be built externally and linked from each page so design changes can be made just once and then applied to all pages.
4. Don't Be Restricted to HTML Text - You Need to build your own graphic headers
There is no way to be a successful web-designer without some proficiency in Photoshop.
5. Organize First - Design Second
It's much easier to decide on the front end how everything will be linked together and how you will keep all your files and directories organized. This is IMPERATIVE for large sites or sites where multiple people will be working on them.
6. Go to the Edge
Keep your body margins at "0". It's another mark of professionalism.
7. Don't Use Frames - Don't Use "Counters"
Search engines can't handle frames and will often bring visitors straight to pages which are supposed to be embedded in a frame. I've never seen a "professional" site with a web counter.