Balance - balance is the visual weight distribution of objects, colors and space in your design. Keep in mind that it isn’t necessary for a design to be symmetrical in order to be considered balanced, and asymmetrical design can also be balanced. For example, with symmetrical balance you would have one element on one side and the same element on the other side. Instead, with asymmetrical balance of the design is achieved entirely by placement of the elements within the design.
Contrast: Contrast in design is an accentuation of the differences between elements. Applying contrast to a design allows you to emphasize or highlight key elements. Although contrast is usually applied using opposite colors, contrast is in fact a juxtaposition of various elements of design, so even differences in textures (rough vs. smooth), shapes (large vs. small) and lines (think vs. thin), just to name a few, also create contrast. The difference between the elements is what creates the visual interest.
Repetition: Repetition strengthens a design by repeating elements throughout the entire piece. It is a conscious effort to unify all parts of a design. This can be a particular format, a color, a shape, a bold font, even a texture — by repeating the element throughout the design you are creating consistency and continuity.
An example of where repetition should most certainly be used is the business package. By repeating certain elements throughout all the pieces that make up a business package (business cards, envelopes, letterheads, etc) you are solidifying your brand image and creating consistency.