GMP stands for grey market premium. It is the amount, over and above the issue price, that traders are willing to pay or ask for to trade IPO shares. The GMP can tell you how an IPO will perform on its listing day.
If you are applying for an IPO, take a look to see what could happen on listing day. But remember GMP shouldn't be the only factor influencing your decision on whether or not to hold or exit the stock.
If you are an investor, then we would say take the GMP with a pinch of salt. A factor as volatile as GMP can't be a deciding factor.
Therefore, you should never apply for an IPO just because it commands a good GMP. You should apply for an IPO because you believe in the company's earning potential. Hence more weightage should be given to the fundamentals of the company.