it's difficult to say without seeing the site, but here are a few things that may help:
1. think about who is visiting the page, exactly what information they need to convert, and exactly how you can get that information across to them in the best way possible to get them to convert.
2. what possible roadblocks are there on the page/site which may be causing people not to convert? remove these - 1 at a time - and measure whether there's a positive/negative impact on your numbers.
3. as above, but with 'features' of the page/site: test different features (eg. copy, headlines, navigational elements, placements of images/conversion buttons), &c. and measure whether your conversions are moving up or down.
4. get visitors to provide their email address & opt in to receive email from you wherever possible. that way you can repeat market to them & increase your conversion.
5. figure out a way of getting non-buyers to tell you why they aren't buying, so you can fix the problems. This could be (for example) by giving them a free chapter of an ebook in return for them answering a few questions that will help you to understand their behaviour.