I try to build on what the student already knows by letting them work as much of the problem/s as possible, and I try to coach them through the rough areas.
I do not like to give the student material that they are not quite ready for, but sometimes this must be done to get a stuggling student through a tough class. When this happens I do my best to simplify complicated topics so that the student can more easily understand the concepts.
References are available upon request. I also offer chemistry, physics, and standardized test prep (SAT, ACT, GRE, etc.).