Every once in awhile, I sit down at computer to write an article or copy for an ad, and nothing happens. A dozen or so, false starts later, a topic is finally decided on, and words just won't come. Only a paragraph or two gets written, and it's time to call it a day. Later, looking at what was done, I usually highlight it, and hit "delete" key.
Other times, words flow as if from a "magic spring" and before I know it, article or ad is complete, but far too long. I try to keep articles around 700 words, as ones much longer seem to drag, and quickly loose readers interest. Effective ads should be four to six lines with 65 characters per line.
Then comes painful task of trying to shorten it. But, you may think, everything is important, and you can't cut a word. But, you must, and will usually wind up with something that at least makes sense.
Many people, who write copy advertising their product, have same problem. They feel they have to give every last detail about their offer in their ad. Nothing could be further from truth.
You should try to give as much information as possible in shortest amount of space. I know this is difficult, but fact is that most people simply won't spend time reading a long ad. Don't worry about length at first. You should get all important points down first, and then try to shorten it.
Do this for five or six ads. Then have someone, preferably someone who is not familiar with your product or service, read them. If you have six ads, have them rate them on a scale of one to six, with one being best in their judgement. Try to get others to do same type of rating. Be sure not to share ratings by other people who did this, until after current readers rating is complete.
There may be a wide difference in ratings, but some pattern should show up. Take highest scoring ad, and run with it. If it draws business, leave it alone. Don't feel you have to tweak ad every time is published.