Identify your student's learning style. Most students will grasp abstract concepts better if you can put them in terms that caters to their way of thinking. For instance, for a kinesthetic learner, you may need to use manipulatives to bring concreteness to abstract concepts.
Be sure that all previous concepts have been understood. Going over basic math facts will ensure that your student has not been left behind in certain areas. Go over all basic functions such as operators, order of operation and fractions.
Bring abstract learning concepts into concrete realities. Write "x=8" then try cutting the variable letter lower case "x" out of construction paper, then cut 8 puzzle pieces out of it to show that "x" represents "8." Then have the kinesthetic learner put together the "puzzle."
Enlist help such as hotmath's online pre-algebra learning library (see Resources below) or videos such as "Video Tutor--Pre-Algebra." These tools will help those students who are visual learners grasp concepts in a way that caters to their gift set.
Understand what motivates the student's learning when you tutor him. For example, if he's interested in checkers or chess, make a basic algebra problem dealing with finding the number of squares by multiplying the number of rows by itself and setting "x" equal to the total squares on the board.