I believe that working through huge numbers of sample multiple-choice physics problems should be a major component of a Physics GRE preparation. You probably have not had nearly as much practice with multiple-choice physics problems as you have had with traditional textbook problems. However, the Physics GRE is 100% multiple-choice questions. Below are some suggested steps to preparing for the Physics GRE with multiple-choice physics problems. You may want to follow these steps with groups of random problems, groups of related problems, or with one problem at a time.
Step I - Try to solve the problem(s) as if you were actually taking the exam. Try to quickly solve it and if you can't figure it out then try to quickly eliminate as many answer choices as possible and then make an educated guess about the correct answer. You may want to read the discussion - Testing Answers and Exploiting Answers.
Step II - Work through the problem as if it were a homework problem. However, before doing this, you may want to read the discussion about unfamiliar subject matter. If you are familiar with the subject matter, then you should be able to work through the problems with some combination of more time, references, or help from others. After you arrive at the solution to the problem, you may want to revisit the question and try to think about how you would approach it again if you wanted to solve it in the shortest amount of time.
Step III - You will want to study material that is related to the particular problem. For example, if it were a mass-spring problem then you will probably want to study material covering springs and pendulums or broader yet, study simple harmonic oscillations.
Side Note: While you are studying related material, it may be helpful to try and create your own multiple choice test questions that cover the material. However, be sure to remember that the Physics GRE test covers problem solving skills and not test creating skills so you don''t want to waste too much time dreaming up problems. However, there is nothing wrong with spending a little bit of time trying to get into the heads of test writers.
Please keep in mind that, like everything else on this website, the steps above are just suggestions. Regardless, most physicists would recommend that you solve lots of practice problems. Come to think of it, you may even want to post signs around your dwelling spaces that read, "Have you worked through any practice physics problems today?!"
Note: If ever have trouble with a certain problem then perhaps you might participate in the Physics GRE Forums and see if another member might be able to help.