Have you taken that first practice test?

I echo what Rich says about taking the GMATPrep - just use one of the two free practice tests it will give you an indication of where you stand and if you do end up studying for several months you can retake that test since you will have forgotten the exact questions after months of studying.

As for what to do once you have the results: you will likely need to do a comprehensive study plan. Few people are able to just address their weaknesses. Even someone who has a talent for Sentence Correction or Algebra will definitely benefit from studying those subjects in-depth.

The Official Guide for GMAT Review is a great book to have, but I look on that more as a set of official practice questions to use when you are implementing the strategies you have learned.

You can self-study with a complete set of strategy guides or you can use one of the many courses out there that help guide your study.

I recommend taking the practice test first, if you are within 100 points of your goal then you can likely self-study your way toward that 740. If you are at a lower starting point you may need some assistance to reach your lofty goals!

Hope that helps you to think about your first steps.

David