As a web developer, you'll often find yourself in situations where rather than build something from scratch, you'd be much better off using material someone else has already put together. This is one of those times. The following material is from the resource links you'll find below.
Generally, all the following principles of design apply to any piece you may create. How you apply those principles determines how effective your design is in conveying the desired message and how attractive it appears. There is seldom only one correct way to apply each principle.
Balance – Visual balance comes from arranging elements on the page so that no one section is heavier than the other. Or, a designer may intentionally throw elements out of balance to create tension or a certain mood.
Proximity / Unity – In design, proximity or closeness creates a bond between elements on a page. How close together or far apart elements are placed suggests a relationship (or lack of) between otherwise disparate parts. Unity is also achieved by using a third element to connect distant parts.
Alignment – Alignment brings order to chaos. How you align type and graphics on a page and in relation to each other can make your layout easier or more difficult to read, foster familiarity, or bring excitement to a stale design.
Repetition / Consistency – Repeating design elements and consistent use of type and graphics styles within a document shows a reader where to go and helps them navigate your designs and layouts safely.
Contrast – In design, big and small elements, black and white text, squares and circles, can all create contrast in design.
White Space – Designs that try to cram too much text and graphics onto the page are uncomfortable and may be impossible to read. White space gives your design breathing room.