Diana has a unique playstyle when it comes to farming and trading during the early game. Her W has a strong impact on the wave and she will tend to push the wave with it. Try to engage and fight her when her W is on cooldown.
Diana is dependent on landing her Q for the all-in. Try to back away if she lands it to reduce her chances to follow up with her E and trade.
She is a melee champion that struggles against ranged champions. When playing as a ranged champion, use your abilities and auto-attacks on her when she moves forward to last hit.
When she is low on mana, she is not a threat to you as her kit requires a lot of mana to trade effectively. When she’s low, there’s your chance to fight.
During team fights, Diana's kit offers a lot of burst damage thanks to her Ultimate R. Try to poke her down before she engages to make it really hard for her to engage and kill anybody.
Diana's engage is pretty scripted. Ward to the side when sieging an objective so she cannot surprise your team with an all-in
Once Diana hits level 6, she can start to receive ganks from her Jungler as her Ultimate R deals a lot of damage and is CC. With this in mind, try to ward the river and side bushes to spot the enemy Jungler before they show up in your lane.
Whenever Diana lands her Q, she could look for the all-in thanks to the reset on her E. Try and play safer when her Q has landed and wait for it to disappear before walking forward.
Diana is rather weak if she doesn’t get kills early on. With this in mind, try not to feed her and ping whenever she goes missing as Diana will look to roam if she can’t kill anyone in mid.