Trending @Cognizant; Need advice: Should I serve NP now or not?

I have received an offer letter from LTIMindtree and need to serve a notice period. But worrying about offer revocation. If I resign in my current company and the offer from a new one is revoked then I will be regretting it. Please suggest the path I should follow and any advice if you have it for me. Also I need to negotiate for my 90 days notice period then how can I? Any tips on that? My joining is in 2 months.