To three bet light successfully you have to remember these three things:
#1: Look for players who are playing too loose and aggressive and opening lots of pots. It’s even more likely that they’re weak if they’re raising when it’s folding to them in late position.
#2: Three-betting light from the blinds is a common play but it’s even better to do it when you have position on your opponent since you’ll keep that position for the rest of the hand if he calls.
#3: Don’t three-bet light with easily dominated hands like weak aces because you’ll get stuck in tricky spots after the flop if they call. Instead, three-bet light with sneakier hands like suited connectors.