In order to create an attractive ad, make it something like this: 1. Easy to understand, 2. Eye catching, and 3. Specific. This will eradicate doubts for customers.
An ad should be attractive to you first so that it can be attractive to the targets.
The ads are supposed to be simple and colorful to everyone; be they targets or not.The keywords are also important, unique keywords will work best. These are the words which haven't been seen several times on the net, but they should be relevant to what you are advertising.