I recommend you keep your copy… short and sweet.
Now don't get confused; long sales copy websites almost always sell more than "short copy" sites. But…
WITHIN your long copy, keep everything short; specifically, I mean you should keep your sentences and your paragraphs short.
A paragraph in a sales letter should be no more than 3-4 sentences long – and they should be short sentences.
People will read more of your copy if the sentences and paragraphs are short.
This is especially important on the first page (or the first screen, if it's online) of your sales letter, when you are trying to draw them into your story.
Don't scare people off with big blocks of text.
Short and sweet is best.