Well, keeping the discounts coupons for customers is a good option.
However, I would suggest you to keep the discount coupons in such a way that you can maintain the profit margins for your business. The reason for this is the fact that you will be able to provide good quality service to your customers only if you have enough profit margins
Also, in order to get more customers, you can keep some affiliate programs for your existing customers and offer them some sort of commission if they bring customers to your company. This should increase your sales and you will be able to keep your existing customers happy