Check your sales data for two years. You will find that a few customers (corporates mostly) buy now and then from you.
Those few customers are your "A" customers.
Though they are few in number, they would have given more than 70%
of your business.
FOCUS on them. Meet them frequently. Ask them about their requirements.
Give them some extra service. Feed them information about new products. Give them those pamphlets lying in your sales desk! Don't let your grip on them go away.
Your business is sure to prosper.