Keep it simple as you may only have a few seconds to make an impact on the viewer and as a result, the advert must be able to convey the message in a small amount of time.
By keeping your ad's concept and wording clear and concise, you increase the likelihood that the viewer will actually get your message. Remember, if the viewer can't easily and quickly understand what your advert is saying, it is unlikely he/she will respond to it.
Emphasize the benefits and not just the features - more than anything else people want to know how your product/service can improve their lives or benefit their company by using your services or product.