Let's say low (IV/HV) < 0.5 Or when VIX is at 20-30. These kind of lows. And buy medium term options. By that I mean 3-4 months until exp.
Buy if you think the underlying will move enough to offset the debit paid for the options. IV doesn't matter.
I told you. If VIX < 30 then it's low. Kappish ? So 25, 20, 15, 10, 5 is low. If 5 is low. Then 2.5, 2, 1.5, 1, 0.5 is low. If 0.5 is low. Then 0.45, 0.4, 0.35, 0.3 .. is low.