Good question. And some great answers straw-people! But why stop at the question.
Politely, and in good jest (and a bit serious) - put your money where you mouth is - log into your broker, and place limit orders ready to go at a price you're willing to buy. The *dip* will either trigger it, or not. And once in play, you'll treat the action more seriously! (you can always adjust - changing one's mind is ok!)
Beat your own brain/emotion at its own game. So many times I've told myself "I'll buy on a dip" and then the dip *happens* and I justify to myself not buying for some reason, only to watch a great company rise on to further greatness.
It took time, but I beat that internal brain most recently with ASX:PME... topped up on its dip.