I think we have all been guilty of not keeping in contact with all of our clients. You should really communicate weekly with your top clients, and monthly with the smaller ones — and a phone call would be best, with email being second best. Of course, everyone should be getting your bi-monthly newsletter, but it’s the personal touch that helps your clients stick with you for a long time.
Remember, they don’t care how much you know, until they know how much you care!