It isn't easy to be a good deputy ... an effective second chair. On the one hand, you must represent your leader to the staff and on the other, you represent the staff to the leader.
A primary goal of a deputy is to win the trust of your leader. He must perceive you as his right hand man ... on his side, fighting together ... not fighting against him. That doesn't mean that you are a yes-man; often, you will find that you have a different opinion. How do you disagree without being disagreeable?
A secondary goal of a deputy is to win the trust of your staff. They must perceive you as their representative ... their voice to present their views and interests to the leader. Are you then a double agent? A two-headed snake? How do you balance this with your primary goal?
The key is to know when to put on which hat. When you are with the staff, you represent the leader but when you are with the leader, you represent the staff. What about when you are with the leader and the staff? Ask, "What is the occasion?" If it is to present a decision then wear the hat as your leader's assistant. If it is for discussion of an idea, be yourself!
As mentioned above, the staff must perceive you as their representative. They must see you in action ... in situations where you are not afraid to speak your mind (even your views are contrary to the leader's). The staff must sense your commitment to them.