This article outlines some of the basic graphic design principles that have been applied for decades.
Less is More
In design, simplicity is more pleasing to the eye than complexity. Before you add a design element to the mix, ask yourself how important that element is and if the element adds or subtracts to/from the overall value and appeal. Use your background as space in your design and move things around in the foreground. You want to achieve an overall balance in shapes and forms.
Rule of Thirds
Sometimes symmetry can be harmonic and pleasing, but in many areas like photography and illustrations, putting your subject dead-center can generate boredom in the eye of the viewer. Asymmetric graphics can look more vibrant and stylish, if the composition is nicely balanced. The Rule-of-Thirds gives you a grid where you can place your design elements and your design will look balanced and harmonically. Divide your image into 3 evenly spaced rows and columns (9 sections total), and place your elements onto the intersections of the 2 horizontal and 2 vertical lines (between the sections).
The resolution of an image refers to the number of pixels per inch and is usually given as dpi (dots-per-inch). Generally speaking, the larger the image resolution, the clearer and sharper the image is going to be. Web Graphics are typically 72 dpi, while print graphics are typically 300 dpi. Always design at 300 dpi, you can size it down later if you have to (you can’t size up from 72 to 300 dpi).
When designers look at a design, they assign a visual weight to each element. If one element is weighted too heavily, they make it smaller or break it up. A good way of assessing the visual weight is to squint your eyes (vision becomes slightly blurry), look at the design, and see how much space is covered (taken up) by each element. You can use percentages or decimals, just make sure they all add up to 100 (or 1.00 for decimals).
An image is like a musical symphony, carefully composed of different design elements. Composed correctly, the combined elements give the image a unique look and feel, something all artists strive for. Use the Rule-of-Thirds and the visual weight of the elements to put them in there right place. Cutting off an element (going over the border) can create a feeling of infinity (continuity). Repetition of certain elements (in different sizes) can help bind everything together under one theme. Playing with font types and sizes and choosing the right one is important and can either add or subtract value to/from the overall graphic. Listen to your instincts when moving elements around on the canvas, see what feels right to you. Chances are, if you like it, other people will like it too.