Use
simple sans-serif fonts (Arial, Verdana) for the body of the document, they are
easy on the eyes.
Don't distort pictures, crop/resize them in Photoshop.
Don't allow text to (almost) touch pictures or areas with a different background color,
create some white space between them.
Don't use underlined text if it's not a hyperlink.
Don't leave an empty space in the middle or at the top of the page, it's where the visitors' eyes go first.
Use only light colors or watermark (faded) images in the background and make sure text is easy to read on top.
Don't use very large fonts for the headings and/or the body.
Spellcheck the page.
Use harmonious colors chosen from palettes built using online tools.
Add a copyright line at the bottom of the page to create a visual clue for the end of the scrolling.
Align elements on a page along common vertical and/or horizontal lines for a tidy look.
Avoid centered designs, they are good for older or romantic moods, but left aligned and asymmetrical designs are cooler.
Pick up an appropriate color scheme for the topic, a zen/spa atmosphere needs a light background and airy layout, a rock band website benefits from a reverse-video setting with a dark background.
Design for an approximately 970 px screen width, using a div container (layer) that you can center for dividing the leftover white space on larger displays.
Keep the design sober by avoiding useless animations, marquees, background songs, etc.
Create a focal point for the page (an interesting picture, a brighter
colored area) to capture the visitors' interest right away.
Create contrast in larger areas of text through the use of italic,
bold, different sizes of fonts and serif (for titles) / sans-serif (for
blocks of text) typefaces.
Avoid using more than 3 font families on a page/site.
Learn and use the box model in CSS and take advantage of the border,
padding and margin properties.
Use relative paths to your resources and test your website on a mobile
device (has no C: E: H: etc. drives)
Left-align fields on a form and don't make them much larger than the expected input.
Right-align labels for the fields on a form, this way they are close to where the user input occurs and easier to read.
Change the text on your form buttons, "Register Now" is more inviting than "submit", "Clear Form" better than "reset".