Learn basic HTML tags even if you use a WYSIWYG web editor like Deamweaver or FrontPage. Knowing the fundamentals will pay big dividends when something goes wrong, as it always does. You can learn a lot by viewing the source of well designed pages that you find on the web. Get in the habit of reading source code online.
Avoid using frames if at all possible. Frames are often very slow to load, The BACK function on browsers may not work correctly with frames, they prevent useful book-marking of your sub-frame pages, some users with smaller screens may have difficulty in seeing some of the material in any of the frames, it is easy to print the wrong frame, and they are frequently difficult or impossible for search engine spiders to index. See more...
If you have to use Table tags for page layout, use percentages for the widths so your pages will resize gracefully for different viewers screen resolutions. And keep the tables as small as possible to speed up downloads. If needed, divide a large table into a number of small ones. But, look into CSS2 for much better page layout tools.
Keep the download time of your pages short - not too many graphics, sounds, or movies. Your home page should not be any larger then about 50K with all the associated image (or other) files it calls.
Think of the people who will be reading your web pages and have pity on them. Writing your pages as if they were meant for your dearly beloved grandmother is not a bad strategy.
Organize the structure of the information on your pages using the hierarchical H1, H2,--> H6 Heading tags. This will help you construct a more organized page and helps people using screen readers, PDA's or cell phones with web capabilities. More and more, search engines expect proper heading organization to get you good placement.
Place all font specification in a CSS Style sheet. Make your font sizes relative so people with reading problems or specific font preferences can override them.
Always include the height and width attributes for your images, This will make your pages appear to load faster.
Always include the alt attributes for your images. (i.e.: alt='"Company logo") Do this because; it is necessary for valid code, users can see the alt description while the graphic is downloading, some users have image loading turned off in their browsers, and for screen readers (instead of browsers) used by the blind or other special case users.
Use .GIF's for graphics (drawings, charts) and .JPG for photo images.
Make sure any digital pictures you use are well cropped and compressed before you put them in you web pages. Otherwise you are wasting your server storage and your viewers download time.
Don't copy others peoples work without permission. Copyright infringement is illegal.
Use text links and keep the default colors if you can (everybody is used to them, and know what they mean). You can add graphic links too if you wish, but only in addition to the text links.
Learn to use CSS styling and style sheets. You will have much better control over the look of your pages, it is a lot easier to change, and it is the way of the future web.
Learn and use the meta tags. They are necessary for accurate decoding of your page and sometimes helpful for search engine friendliness.