what recommendations does grantiano make to play the fool (lines 79-102)

Grantiano sees that Antonio is looking rather glum. Grantiano's advice is to play the fool (not take things so seriously) and live a happier life. He says that men so serious are silent because they have nothing worth saying. Grantiano adds that over serious men get sick, "Sleep when he wakes, and creep into the jaundice by being peevish?" This guy is pretty laid back. Playing a "fool" here is not a bad thing. Grantiano feels it a natural progression for a happy life,

"Let me play the fool.

With mirth and laughter let old wrinkles come.

And let my liver rather heat with wine

Than my heart cool with mortifying groans."

Hey, this is actually good advice!