What's the best way to study the GMAT or GRE, solve 2000+ questions or analyze techniques and only solve the official guides?

The right answer depends on where you are in your studies.  If you're pretty close to your target, (30 points in GMAT and under 700, or 2-3 points in GRE Quant or Verbal), you're probably fine to just do practice questions. However if you are aiming for 730+ in GMAT or 333+ in GRE, you will need to take a more systematic approach. Go a little more into the theory of the questions and analyze the exact methodology of how you are solving the questions, every step of the way.  The best way to tell how well you've learned something is to teach it.  If you can explain it to someone else and they get it, then you get it.  If they're confused, you may get it a little, but you don't fully get it.