Make sure your explanations are clear. Make sure your writing is neat, easily readable, and clear. When the student demonstrates an understanding to your satisfaction, assign 2 or 3 similar problems. Should the student not show understanding, redo your explanation, preferably with different problems. This time, however, ask the student at each step to tell you what you did.
Time is of the essence.
Do not spend too much time with any one student. Keep each session from 30 minutes to an hour or 30 minutes only if there are students waiting. Break each session into smaller intervals. To save time, work in groups of three with students who are having the same problems. Avoid errors by not rushing.