I see so many pictures destroyed lamps, furniture and loved ones that I thought I'd pass this tip along:

It doesn't matter how much muscle energy you 'impart' into the grenade to get a good throw. All that matters is the amount of velocity it is moving in when you let it go. And the easiest way to do that, which is way faster than using your whole arm, is to move your hand in a whip-like fashion and let the grenade go at the arc where it has the highest velocity.

Straight from the horses mouth:

JamesButlin - Today at 5:26 PM

it transfers the velocity and rotational velocity to the grenade when you let go so if you can get enough speed with a small flick it'll do the trick

JamesButlin - Today at 5:29 PM

the grenade gets a little boost of velocity than what it'd normally get IRL so we don't have to full on throw with all our strength

tl;dr Do this flip with your hand, but with your arm stationary, just the quick wrist flip

http://www.xbadmintontricks.com/wp-content/uploads/2014/01/01-serve.gif