Maokai is at his weakest during the early game. Look for an early advantage to force him to miss out on gold and XP.
Once Maokai is level 3, he can start trading with you once he has all of his basic abilities. Try and get him low so he is unable to look for a favourable trade.
Avoid standing towards the top side of the lane if you know he’s placed Saplings E in them. However, you could walk towards it before running away to “bait” out the Sapling E.
Avoid fighting in the jungle as that will allow Maokai to get a good Ultimate R off. Additionally, avoid fighting around neutral objectives like the Dragon or Baron too.
When sieging, make sure no one on your team is too far forward as Maokai can isolate them and catch them out of position with his W.
As it might be hard for Maokai to team fight, he may try to flank from the side to make it easier to get on to the enemy. He may also use his Ultimate R from the side to CC your whole team. Ward the flanks so you can spot him before he initiates.
Once level 6, Maokai’s kill pressure in lane will increase. At this time, he might start getting ganks as his Ultimate R is a great tool for initiating ganks.
At level 3, Maokai can start to play more aggressive as he will have access to all his basic abilities.
Maokai is good in team fights as his Ultimate R has a large area of effect. Make sure you split up or disengage as soon as you see him so he is unable to utilise this ability.