Think long-term. Deep client relationships are built over time and are difficult to dislodge; instant friendships can disappear just as quickly.
Be thoughtful. Personal touches show you see them as more than just a client. Remembering their child's name or recommending a hotel as they plan a holiday suggest you are interested in them, not just their budget.
Give extra advice for free. This makes you more of a friend than a salesperson - they may well feel that they owe you one as a result.
Listen, listen, listen. This will make them feel good and give you important clues about their hopes and fears.
Help make them heroes. If you can remove some of their stress and let them take the credit in their organisation, they will be keen to work with you again.
Keep them informed on your work. They won't want surprises, and if anything goes wrong they must be the first to know.
Lead opinion. Challenge constructively when you believe your client is in danger of making a mistake. Good friends tell you when you are going wrong. So do good advisers.
Keep your ear to the ground. Staying close to the winds of change in their organisation will enable you to give your client good counsel and position you to pick up additional work.
Make introductions. Introduce your client to people who matter in their world so they feel that they are part of an inner circle.
Stay in touch during the fallow periods. Fair-weather advisers will evaporate and you will be the one who is remembered and trusted when the good times return.
Nothing beats doing a good job. If you deliver an excellent service the relationship is sure to deepen.