I get this question very often, more often since i work with a few clients known to be very very difficult. The answer is not so difficult though. You must realise client knows his business very well and you must respect him for that knowledge, business has dimensions that you may not be aware of, so his/her decisions have to balance so many things besides leading business towards profits. In his mind what designers do is only a piece of a jigsaw puzzle that needs to fit in. For us designers, our life rotates around what we do. So when you are explaining your work to client, you need to fill the gap between his thinking and yours.
This means you start with what you have understood about his business and “the role of what you are doing” in those plans. If there is a misunderstanding in this , do not proceed ahead..understand that you need to get this right first. and explain to him before you show how your work will fit into his concerns. It is also prudent to explain where it will fall short. Clients may expect unreasonable feats to happen by design, we know design wont do that.
When explaining your work, keep away from jargon, trade-words and adjectives. Try not to build a expectations from what you are presenting. By the way…advertising agencies always use super adjectives to ump up their work. It works for advertising since the expectations are limited in the sense..you know what you will get. Design concepts on the other hand can be difficult to grasp at first.
Be patient with the client, explain all you have to explain and then take their questions. Ask for specific reactions, and then either defend your work or agree to change. Do not defend un necessarily. If their is something you did not consider before, accept it and also accept that it would change your concept.
Be honest and let the explanation come from heart, now it wouldn’t come from the heart if you are not convinced about it. So first thing obviously should be that do not present something that you yourself are not convinced about.