Here are some design principles that you can use to guide your own design process.

• Design for the intended audience, not yourself.
• Create a clear visual hierarchy. Do preliminary designs using a grid. Consider the white space as an element. Treat text as a graphical element.
• Pay attention to Navigation. Make your navigation consistent and visible (but not overwhelmingly so). Keep people oriented (breadcrumbs, site maps, descriptive links, titles, etc). It's easy to get "Lost in Hyperspace".
• Usability: What do users expect? Follow conventions where it makes sense -- don't intentionally break common practice without reason. Make it easy to read and scan. Avoid long line lengths -- no longer than 50-60 characters per line. 7 plus-minus 2.
• Minimize noise (in most cases). Omit (unnecessary) words.
• Resist specifying heights. You're almost always better off planning the horizontal space carefully, and letting vertical space expand or contract as needed. Fixing heights leads to errors when the content overflows the expected size (such as when the user enlarges the font size in their Web browser beyond what you expected).
• Pay attention to use of Color. Colors have symbolic associations that contribute to the "feel" of a site. Some people are color-blind. Many color associations have a cultural basis, and the typical associations listed here probably reflect a Western bias.
• Red: Vibrant, passionate, love, war. A very strong and attention-grabbing color, red is charged with emotions.
• Violet: regal, sacred, sensual. In deep shades, violet is luxurious. When lightly tinted, it is aromatic and spiritual.
• Blue: Cool, dependable, sophisticated, sky, water. Blue is full of depth, constant yet dynamic.
• Green: Fresh, relaxing, earth. Green is very balanced and calm, a natural color.
• Yellow: Sun, energy, warmth. Yellow is welcoming and full of life, a happy color.
• Orange: Strong, vital, hot. Orange is the warmest of colors, a healing and playful hue.
• Symbolic meanings are attached to shapes (here is a discussion by Molly Holzschlag).
• Rectangle: rectangles and squares typically represent authority, stability, and strength. Many designs attempting to convey reliability and consistency will use lines, rectangles, and squares.
• Circle: circles and curves typically represent community, fluid movement, and the feminine.
• Triangle: triangles represent action, movement, and direction, and are associated with the masculine.