Don't catch a falling knife... At least wait for it to trend sideways for a bit. Now there is the possibility of further cascading falls, but if you see it go sideways and then start to trend up, or solidly tick up for a while or significant percentage then you can at least kid yourself you were buying in on an upswing.

If you're worried about buying back in too soon then do multiple buys - 50% now and if it goes down further buy more later and average down. If it starts shooting up buy more on the way up - at least you can get some of the low price.