Customer Service 101. Smile, listen, service.
1.) Smile. People want to work with happy people. I know it sounds simple, but it matters. Even if you are having a tough day, a smile can trick you into feeling better. ;-)
2.) Listen. Before you propose the solution, you got to take the time to hear all the sides of the challenges your client is facing. Take the time to understand the desires from your client, then you qualify yourself to provide valuable solutions.
3.) Service. Whether is it a product or service you are selling, make sure it fits the customer's challenge. Every client and every project requires a different solution. If problems arise, diffuse the problem while keeping the structure.
This is what works for me, share what works for you.