When I learned copywriting one of the strategies I was given was to create a swipe file.
That is find successful promotions, sales letters and emails and learn from them. As far as I can tell all the great business copywriters do it. I know that Joe Vitale has a collection of successful promotional material stretching back into the 19th century.
My collection measures about 2 metres on my bookshelves and if I get stuck then I go looking for help. Of course you're not going to copy word for word what other people have done. Not ethical and in the long run stupid. But the ideas that the material contains can jump start your imagination and your writing.
Why re-invent the wheel when there are such great guides out there for you to learn from.