Hi there,
Sorry to hear of the challenges you dealt with during your previous GMAT preparation experience. Hoping things go better this time! As someone who taught and tutored hundreds of GMAT students and oversaw GMAT curriculum for a while, I would offer the following suggestions:
-2-3 months IS the ideal study timeframe I recommend. No more than that! You don't want to get burnt out or tired of it all.
-I strongly recommend a reputable GMAT prep course and/or private tutor. It makes a ton of difference to have proven test prep, materials, and realistic practice tests. Additionally a tutor can WATCH what you are doing and suggest specific steps for YOU to take in a way that even a classroom doesn't often offer.
-Be sure to diagnose the areas and question types you need the most help on.
-For quant, be sure you are comfortable with your content and the basics first; consider something such as a GMAT Math Workbook to brush up early in your prep.
-Be sure to practice as much as possible ON THE COMPUTER as that experience is different from the feel of doing q's in books/on paper
-Do 5-10 full length practice tests, and REVIEW each one you do (the next day) to learn from that
-Prepare mentally to take the test more than once.... it's quite common to do so, and there is no down side for doing so; if you do find you want to try a 2nd time, do it asap (as soon as you are able to) as your mind will still be fresh.
Keep us posted on other q's and good luck!