This is cumulative, and you'll get this through normal progress.
Some tips for hitting hard:
Luck should be equal to your base stat (DMG for active and DPS for idle builds); LUCK = crits, and 50 LUCK seems to be 50% chance of a crit. As well as getting more gold and keys, for more efficient progress, well, you know what doubling your hit power does!
An active build with an autoclicker is so, so, so much faster than any idle build ever will be. There's no reason you can't progress with DPS/idle, but unless you've got a good reason not to go for DMG/active, split your points between DMG and LUCK.
Weirdly for a damage dealing guide, I'm going to suggest never touching the second weapon, and using a shield instead. "Defense" and "Armour" only increase your HP, and they don't do it as fast as you will be progressing. Shields actually reduce the damage, so you can be fighting harder fights, getting more gold and thus hitting harder without worrying about HP. You will reach the point where you're absorbing all damage way, way, way before you reach the point where you're killing the monsters before they can hit you.