However, you can't move from being a stranger straight to being a best friend or customer.

So it's important to put at least as much effort into your plans for keeping in touch with existing customers as you do for attracting new ones.

One of the main advantages of developing long-term relationships is that it's typically six times more costly to sell to someone new than to an existing customer.

But, of course, it's one thing to know the value of building long-term relationships and another to follow the steps required in order to do so.

Here are seven steps to turning one-off customers into valuable client relationships.

1. Concentrate on getting the second sale

Ultimately, people are only customers if they buy from you regularly. And many people will buy from you once and never again. So, to turn someone into a genuine client, the most important thing is getting the second sale from a new customer - and getting it as soon as possible. Following the second sale, you are more likely to keep them as a long-term customer.

2. Always act in their best interests

According to Kevin Hogan's book 'Psychology of Persuasion', people are more likely to do what you ask if they believe you have their best interests in mind. This is the 'Law of Friends'. So, to build a business relationship, you need to show clients that you are looking after their interests. You can normally only do that over a few weeks or years, in the same way as in a personal relationship. One step is to stop worrying about getting clients to like you and focus on looking after them. As 'Built to Last' author Jim Collins says: "Don't be interesting. Be interested." That helps you think of them as individuals.

3. Keep in touch regularly

You can build trust through a regular newsletter which gives valuable information - rather than simply promoting your services. You can also build regular contact through articles, podcasts and teleseminars.

4. Make your contact personal

To make your contact with customers personal, you need to learn about them. You can start by just listening to them - for example by posting a survey on your website or sending out a customer questionnaire. The more you know about their likes and dislikes, the more personal you can make your services - for example sending them clippings you know will interest them or recognizing their personal achievements and family events.

5. Recognize that satisfaction is not enough

People will not stay with you and build a long-term relationship because they are satisfied. They expect that. You need to deliver exceptional service - some describe it as 'customer bliss'. You need to go beyond what they expect - give them even more; care about them more than they are used to being cared about.

6. Ask your customers to help you

Once you have built a good relationship, you'll often get help from your customers. For example, they'll give you feedback on what needs improved or they'll provide referrals and testimonials to use promoting your services. And, not only that, the laws of psychology mean they are more likely to buy from you again after they have helped you in some way.

7. Focus on your most profitable customers

Typically you will find that 80% of your profits come from 20% of your customers. So you need to understand which 20% are most profitable by looking at the Lifetime Customer Value, which is the total amount somebody would spend with you over their time with you as a customer.

Building long-term relationships is no easier in business than in your personal life. But it can be extremely rewarding.