How does one get a upgrade to Gold offer?

I have been plugging away at 26 nights this year and will most likely get to 50 in the next few months IF I continue to stay at Marriott Hotels.  I have a colleague that got the gold offer and I was wondering how one gets this offer?  I am 2 stays away from the Hilton Gold level which is swaying me to book my next 2 trips on their side, but would like to stick with the Marriott brand, if only I was given an incentive?  I may have to make the switch as there are Hilton Hotels in all of the locations I frequent.