Know basic history. You may have a college degree in history, but it's not a requirement. Just know more than who you're helping.
Meet and talk with your potential students before attempting to actually tutor them. Many of them may resent seeing you, thinking they do not need the assistance you are offering. This can also help you see what the strengths and weaknesses your pupils have before you tutor them in history.
Teach your children history at levels they understand. You may have to adjust your teaching of the subject as you learn just what the students know and understand.
Keep your students engaged. Change things up often so you don't lose your students' interest and enthusiasm.
Change the learning environment, if necessary. Don't let distractions exist to take away from your teaching.