1) If possible, use a visual symbol. Remember the Chinese proverb,"a picture is worth a thousand words." Make sure the picture is not just pretty but communicates what you want to communicate.
2) Use different fonts (typescript) and different point sizes (size of the actual letters) for different pieces of information.
3) Be very sparing with words. Put only the most important information in the ad. Name, telephone number and website. Remember a display ad is not intended to give all the information but rather to bring attention to the product and let people know how to get more information.
4) Communicate. It is better to have an effective ad than a pretty one, or one that tells readers everything they did not need to know.
5) Use upper and lower case. Using all capitals makes it difficult to read.
6) Legibility. There are many fancy, difficult-to-read fonts. Use them sparingly
7) Fill the space carefully. Experiment with centering or placing information flush right or left.
This is an example of an ad that violates all of the above principles.