What is the best way to build relationship with client?

We should first start building TRUST. The trust is the platinum standard of service. It is the clue that keeps customers coming back. The customer’s faith in your word; belief in your promises are what saves you in those difficult times when everything seems to be going wrong. Building trust is a succession of positive experiences and certainly not over night. Least we shall ensure FAIR deal that leads to trust building in the following ways: 

They have the outcome they expected – they get what they asked

The process of getting that was painless

You kept the performance promise you made

You treat them ethically - no bait & sneaky behaviour 

You acknowledge their unique wishes if any

Their best interests are placed ahead of the company’s convenience