The key to writing a successful ad is knowing who your audience are and what they want. You should already know your target market before you even consider writing an advertisement. You also need to be clear on what you can offer them and what you are trying to achieve.
Even if you are planning to write the advertisement yourself, you may find it helpful to imagine how you would explain what you want to a freelance copywriter. A good copywriter or agency will always ask you to explain who your advertisement is aimed at and what you want them to do as a result of reading it.
Focus on a single, clear message that you want your advertisement to put across. Then use the headline, an illustration or both to grab the reader's attention.
The simple approach is usually best. A successful headline might highlight the key benefit your product offers, or simply arouse the interest of your target audience. Looking through the ads in the publications you are planning to advertise in should give you a good idea of what works and what doesn't.
Once you've got the reader's attention, the body copy adds more information. Again the key is to concentrate on what your target reader is interested in and what you are trying to achieve.
Big brands sometimes produce ads with no body copy at all: the illustration along with their brand name is enough to convey the image they are after. At the other end of the scale, ads in specialist magazines may include more extensive details for the enthusiast.
Straightforward, punchy writing works best. Keep sentences short.
If in doubt, leave it out. Don't be afraid of having plenty of white space in your advertisement. But do make sure you have given the reader the information they need. It's essential to make it easy for them to do what you want them to do. So make sure you include your contact details, and consider encouraging them to act now by including a deadline.
Once you've drafted your ad, leave it overnight before you read it through. If you can, get the ad properly laid out before you check it.
Then put yourself in the shoes of one of your target customers and have a look at the ad: