I run a web hosting company. Some of my clients' one-year contracts will end in October. I plan to send them a letter asking them to renew their subscriptions and need advice about what to say.
In a highly competitive arena such as yours, you need a strong hook (or offer) to start. Then follow with the benefits you provide, with special emphasis on the benefits that can only be achieved by continuing with your firm. In essence, this point of differentiation should be at the core of your message each time you communicate with customers. And don't wait to communicate when everything is riding on the response to one letter. Touch your customers in a positive way at least every month--and not just with a bill. Make your goal to become an indispensable part of their business success, and you'll see your sales grow with them.