Improve your grammar: I worked very hard over the last year for GMAT...

I worked very hard over the last year for GMAT. Unfortunately I was barely able to cross the 600+ mark. The results were dismal compared to the labour that I had put in. This has shattered my confidence. However, I have picked myself up and plan to give it another try this year. I need some sure-success mantra.

can any one tell me some tips to enrich vocabulary. :?

I would be very excited for those scores. I am planning on spendinfg the next 6 months in preparation but i need help with even the basic, any suggestion. The classes do not help me yet because i am so “rusty”

I think that the attitude you have approaching this second attempt is already a great step to succeeding! Sometimes we are taken slightly off gaurd when it comes to test taking, particularly when it is a very defining exam. Now, though, you have some experience with the format, timing, and sections of the test. This should be helpful when you are going through the exam for a second time. Continue with the rigorous preparation just as you did the first time you were taking the exam and I think you should definitely see an improvement in your scores! Best of luck on your second round!

One way to learn tough words is to create links to the word from various approach, from thesaurus / images / mnemonics etc.
There has been various sites that can help you to practice the new words you learned.