First, congratulate your new client on their decision and reinforce their commitment to work with you. You want to build that bond so tight, your client will never want to let go.

Second, help your new client see that you are not a flash in the pan, that you are making a personal commitment to them, their company, and their needs. Tell them what your future together holds.

To build a deeper connection, ask your client sincerely why they bought from you. Listen actively. They will appreciate your interest and it will be priceless insight into your target market as you reach out to other prospects.

Each time you call or email to thank them for their business you have the opportunity to engage them in a number of ways. Be sure to leave the door open for them to contact you directly with any questions they might have now or down the road. Start a habit of telling them what to expect next: what they'll receive, what you'll do, what they'll need to do, etc. Restate the results and benefits to them that you will deliver on. Set the expectation that you will be in touch in 30 days so even if they don't call you with a question/problem, you are going to make yourself available to them at that time.

We all get unsettled by surprises. It's human nature. Be sure to explain what reactions and surprises your new client may have in the first/next month of using your product or service.

If you don't receive payment upfront with the sale, have an automatic procedure in place to follow-up, confirm, or inquire about payment. That way the process is independent of the personal rapport you have established.

In each subsequent call/visit for the lifecycle of that client, it is part of the sales process to ferret out the client's unspoken concerns and doubts.

When you take these steps and take good care of your clients, they will never leave you. Since it costs 7x more (in time, money, effort) to win a new client than to keep an established one, isn't it worth it to you to pay attention to the details?