Well, since nobody is responding, I might as well share my experience as a chemistry tutor so far (which is basically 1 hr of professional experience).
One thing that is important to know is that you need to prepare before going to see the student (especially if you are asking for money). You might have learned the material before but it might be taught differently than you remember or you might have forgotten some things since you took the course. Ask the person you are tutoring with information about the material they are covering, so it will be easier to help them. I prepared before going, but there are other problems that come up as well.
Another issue is being able to explain the concepts to the student. You may know the information but it can be difficult to articulate yourself to the student when you are asked questions. Practice using the terms you are trying to teach and knowing in what situations they arise, so you do not fumble over a concept that a student is only beginning to learn. This is the main problem I had.
Lastly, I can say these things that came up in the one hour I spent tutoring someone, but the main issue is that no matter how you prepare, the only way to become a progressively better tutor is practice. I would suggest volunteering or tutoring someone you know well and asking them if there is anything you could do that would help them understand the material better. Of course I mainly speak from conjecture and not experience. So if there are any teachers or professional tutors out there please contribute to the thread.