to the original poster -- i'm sorry to hear about your score drop.
could you please provide us with more specific information about your scores? you've given us your numerical scores, but basically nothing else; we have no information about where your strengths and weaknesses lie.
we can't really offer any specific advice unless you give us, at a minimum, the breakdown of your scores into quant and verbal components, along with a brief summary of which areas you found least and most challenging.
the more detail you can get us, the better the advice we'll be able to get back.
--
venkata's response above is right on the mark, except for the following item:
Take as many full-length tests as you can throughout the preparation time.
this is not necessarily good advice. indeed, for a study period the duration of which you have suggested (2 to 5 months), it could actually be quite counterproductive.
--
first, you must realize that practice tests are not as universally helpful as a lot of people make them out to be. in fact,
there are only two main purposes of taking full-length tests (as opposed to doing timed sets of problems from other sources):
1) FIGHTING FATIGUE
2) PRACTICING TIME MANAGEMENT#1 means just getting used to the idea of taking a test for four hours straight -- many students can't last that long at first, and only taking full-length tests will develop the ability to take a test for this long in one sitting.
#2 refers to developing the discipline of time management over the full length of a 37-question quantitative section or a 41-question verbal section.
if FATIGUE and TIME MANAGEMENT are not major issues for you, then there is no reason to take frequent full-length practice tests.if these are not major problems, then you should focus your attention on topic-specific homework sets instead. your choice of topics should of course be
driven by practice tests, but INFREQUENT practice tests are enough to dictate the topics that you should choose for homework.
--
second, you just finished recommending to this student that he/she should follow a two- to five-month study plan!
in order to practically follow the advice to "take as many full-length tests as you can"
over a period of several months, this student would basically have to
* scrounge around every corner of the internet
* buy
any and all practice tests he/she could find, and
* take them all!
the problem, of course, is that
there are lots of really bad practice tests out there.
i also post over on the BeatTheGmat forums, where the requirements for citing sources are more lax and students post sample problems from all sorts of random exams from the internet.
the one thing that most of these "random internet source" exams have in common is that many, if not
most, of their problems are, to put it bluntly, inexcusably bad.
this is especially true in sentence correction, on which i see 3-5 unacceptably poor (if not downright erroneous) problems for every one problem whose quality is worthy of the gmat.
in short,
the pool of QUALITY practice tests is quite limited, even if the total pool of tests is not.
you should conserve these tests, taking them sparingly so that they last for the entire duration of your study plan.