Seeing how real life grenades have a very large radius of effect - compared to most games, at least... There isn't much to do. If you can hide behind something, preferably an overturned table or a wall, who knows. Table probably wouldn't save ya, but a good brick wall might.
Or, alternative, throw someone next to you on top of it and see if his or her body is good enough to stop the impact while you duck away.
Which brings up a question for those who claim to be savvy in fields of real life warfare - would a modern frag grenade, or whatever you call them, blow through a human body in above scenario without any significant change or would it work? I mean, we all know the generic "self-sacrifice" trope that gets used in certain war movies and war books, where some guy jumps on top of grenade to save his buddies. Would it work on modern weaponry?