One of your business's most important assets are your existing customers. They're the ones who've already found and chosen you over competitors, and are familiar with your products/services. For these reasons it's cheaper to focus on increasing sales with these customers rather than attracting brand new ones.
Here are some ways to sell more to your existing clients:
If someone has bought from you before they are a good judge as to what sells well and why that is. Follow up sales with a call or questionnaire to get feedback. Using this, you can construct an effective sales strategy and meet demand more accurately by knowing what they need/want.
Social media is a cost effective way to get customer feedback is to get their opinion on new products/services and check out the competition. If you have an online forum consider implementing a discussion board or thread to gather further feedback.
Further your reach to clients by increasing either the range or value of what you sell. If you sell online, use your website and email marketing campaigns to make recommendations based on customers’ buying habits.
Another way to increase sales is to alert customer via email or newsletter about new, improved or related products/services.
Determine what your high spending customers really want/need from you and encourage them to order. Whether that be discounts or promotions on further purchases.
You can gain new customers through referrals, by giving discounts to the customers who recommend your business to others.
No one likes to be bothered with multiple sales pitches, especially if the product or service doesn't meet their needs. You need to ensure your marketing campaigns are targeting the right customers, otherwise you run the risk of losing their trust and thus jeopardising the relationship. Instead aim to form solid long term association, rather than chase one off profits.