Give your customers a strong reason why you are sending the letter, why they should read it and why they should respond to it now. Example: "Because your interest rate is going up, give me a call so we can discuss your options." "Your credit has improved since the last time we met, let me sow you how you can now save money...."

Using the specifics in your market will give you more credibility. Take the time to really hammer out your marketing to make it the most personalized, intuitive it can be. Your clients will thank you for not wasting their time with garbage!