Keep it Simple – Always remember that most flags are seen from a minimum of 20′ away and are in constant motion. Under these circumstances, the more simple the design the better. Also, the more complex the design the more costly it is to manufacture.
Images and colors should be easily recognizable – Usually, a single primary symbol is best. A simple design such as McDonald’s “golden arches” is easily recognizable and readable from a distance.
Only use two or three basic colors – Always limit the number of colors in your flag to three colors that contrast well. Separate dark colors with light colors and vice versa, a good flag should always replicate well in grayscale. More than four colors make the flag unnecessarily complicated and expensive. Flag fabrics come in a relatively limited palette, so stick to the basics
Keep lettering and seals to a minimum – A lot of lettering is nearly impossible to read from a distance and seals are usually designed to be seen at close range. Very few seals are effective on a flag, they are just too complex. Remember, the more complex the design the more expensive the flag is to make.
Be distinctive – Try to make sure that your flag does not closely resemble another. Remember, your flag will probably be seen from a distance so make sure it stands out as yours.
Other things to consider – A rectangle is the standard flag shape and the width and length proportion should be 1:1.67 (eg 3’x5′) Remember, flags wear. By retaining a rectangular shape and avoiding symbols at the fly end, a flag can be re-hemmed and given a longer life