Tell your audience what kind of support they'll get after they buy. It could be free consulting, tech support, free servicing, etc. This may also answer some of their buying questions ahead of time. People don't want to buy products without knowing you will be there to help if they have problems.
Ask people at the end of your copy why they decided not to buy. This will give you new ideas on how to produce ad copy that's more profitable. Have a web form or e-mail link in place so they can answer you. You may find out they don't like your guarantee or graphics. It could be anything.
Think of ways to get your site or business in the the news. You could sponsor a fundraiser, break a world record, hold a major event, etc. Simply write a press release about what you've accomplished, then send it to media outlets thatcater to your target audience.
Hold a contest on your web site. Give other web sites the option of offering it to their visitors. This'll multiply your advertising all over the Internet. It would become a viral contest. Of course the contest must either be ongoing or held regularly so you could allow other online publishers to offer it to their visitors or subscribers.