1. Don't be clever
The greatest headlines and copy are those that are straightforward and to the point. Use language that you would use in conversation - but be sure it's not jargon (unless specific to industry) or grammatically incorrect.
Don't give in to the temptation that adjectives are winners - they're not. People respond better to verbs. It's quicker and to the point.
An active sentence such as "Tom kicked the ball" is far more forceful, entertaining and effective than "The ball was kicked by Tom". Remember that adjectives are a waste of time.
The biggest mistake companies make is mentioning how great they are and how excellent their services are, etc., etc., ad nauseam. Keep it about the prospect/reader/customer. Write how it can affect them - make it about them.
Also, remove the "I" from your keyboard. Never write in the first person - people are selfish, and are more interested to see what's in it for them.
Get to the point quickly. People don't have all day to read - and there are tons of ads out there. Make yours quick and to the point. It is hard, but that's what copywriters are paid to do: to come up with catchy, to-the-point copy. Remember, one idea per paragraph.
Right, remember this: for every comma you use, you lose R50. Rather use a dash or an em-dash. A comma retards the flow. So don't use too many punctuation marks - and never use an exclamation mark, unless it really, really works.
Your copy should be positive, even when explaining a problem to the reader. At a glance, readers remember the sentence without the "not" - so for example, "Brand X believes in not disappointing customers." For some reason, psychological or other, readers will keep "disappointing and Brand X in their minds" - make it positive.
