How To Develop A Deep Understanding Of Your Customers?

Listen

Observe 

Without judgement

be honest to yourself when dealing with potential customers

Hear what your customer wants, not just listen - and understand what they require. It may be two different things.

Be preemptive and provide solutions in advance if you foresee a problem. Don't just speak to them when you want to sell them something, call them and ask how things are going and is there anything you can assist them with. Be available and helpful, make them feel important to you, let them know you appreciate your interactions with them regardless if they are buying now or later..