Thresh vs Lulu

Open with Flay (E) before Death Sentence (Q): the slow makes the hook much easier to land.

In lane, space out your autos: Flay (E) charges them passively, and the longer you wait between two autos, the more damage they deal.

Don't recast Death Sentence (Q) on reflex: the target is already being pulled toward you, and jumping on them often exposes you for nothing.

Throw Dark Passage (W) toward an ally in trouble before they need it: they can click it to come back to you, with a shield.

Place The Box (R) right after a successful hook: to escape, the target has to break a wall, and the first wall broken slows them and deals full damage.

Dodge Glitterlance (Q): two bolts fly out, one from Lulu and one from Pix, and each one damages and heavily slows.

Engage in two steps: make her use Whimsy (W), then re-engage during its 18-second cooldown.

If you can reach her, focus her in teamfights: Whimsy (W), Help, Pix! (E) and Wild Growth (R) are mostly there to protect her allies.

When Wild Growth (R) enlarges one of her allies near you, back off: anyone close to them is knocked into the air, then the aura slows them.