GMAT Strategy

well,i am a computer guy with high undergrad GPA(infact i was the first) but being out of school for almost 3 years now...i am not being able to do good in gmat...
i have prepared it for almost 6 months now and read almost all the books and took numerous tests but max i was able to get was 590 and my average is around 550 only......which wont go well with my gpa when i apply

till now i have been preparing myself with books,cds,forums(this one is good),videos,tests but it doesnt not seem to do any good...my score was around 550-590 before 6 months and even now its the same

so,i have decided and joined a renowned local gmat institute(they are in this industry from long time now) so i think caliber of the instructors wont be the problem...
but i was not able to arrange special classes and i am attending regular classes...
now i feel, if i dont make any plans it will be kind of revision of rules,simple construction and all...
so
how should i approach it...
should i revise all the things once again(according to course) as if i am new to these matter

should i focus more on my weakness..(time is one) and keep on asking the instructor on that...

i have list of difficult questions(700+) should i focus on those and ask those questions to instructors?

what should i do?please give me suggestions....

if i dont make a preplan i think it will be all same again when i finish the course...i am not taking gmat just because of these classes.....
please help