1) If I were you, I would request an on-board trainning or have an one-month (or couple weeks) of transition when assuming the position.
2) Assume that you missed step 1), I would suggest you'd better to communicate and communicate. You can call an one-on-one meeting with him or a group meeting (engaging him, your predecessor, or his boss if necessary) to clarify or re-align the protocol or business process.
3) Be well-prepared (be clear and be well-thought) before any business meeting.
In the meeting, stay calm yet firm or persistent (no emotional attachment) since it is just business.
4) After for a while, encrouge your predecessor not handle his business call, ask her to transfer his request to you.
5) If these still do not work, you may evaluate to esclate this ...
