Referrals are the best way to do business. When someone has been referred to you, they have more confidence in your product or service and making the sale tends to be easier.
How do we keep those referrals coming? First, do really good work. Second, ask for referrals. LinkedIn actually encourages you to ask your contacts for a recommendation and it's easy to 'recommend' people too.
Let's not forget to thank people for those referrals! After all, they either spent some time composing their referral in writing or they personally recommended you to someone they spoke to. Either way, they trust you enough to pass your name along.