How do you get back into the market during down periods?

I went to cash in December for my equity portion, and now that the markets are down ~20%, I'm thinking about getting back in. I suspect the market will go down even further (I can see a lot of people eager to buy in, so it can't have hit bottom yet, though who knows), but I don't feel comfortable sitting entirely on the sidelines either.

I invest in VTI/VXUS, but I don't want to lump-sum. Is DCA really the best way, or is there a good program for buying on the way down, and the way up again, i.e. assume it will go as low as 50% so put in 2x for every 5-10% drop (VTI drops 10%, put 20% of your equity cash in)? And if the market doesn't keep going down, how do you schedule buying on the way up?