You can run the most visually stunning well-written ad ever crafted, and if it's aimed at the wrong audience, it's not a good ad. I define good advertising as that which moves a prospect or client to action. Action can be picking up the phone, visiting a retail location, or requesting additional information. For tips that will help you in creating ads that will be noticed and acted upon, read on. Know as much about your audience as possible before writing or designing anything.
Advertising is about selling.
The point of your ad is to generate interest in your product or service. You are not trying to win awards, be the next Matisse, or conquer the ad world. Unless you are very capable, hire a freelance designer or agency to create your ads. With the proliferation of desktop publishing tools, many small business owners have started creating their own ads. I strongly advise you not to do this unless you are very proficient.