Avoid standing towards the bottom side of the lane as Maokai will place Saplings E inside the bushes and they’ll deal a lot of damage to you if you’re caught by them.
Make sure you hit level 2 at the same time or before Maokai as he has great all-in at level 2. At level 1, if you’re unsure what ability he has taken, make sure you stand back and out of range just in case he starts W, he can’t gain an early health advantage.
In the early game, try to use your range advantage to poke and harass him down. Try and stay at max range though so he cannot get on you with his W.
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.
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.
Maokai is good at level 2 onwards as he can lock you down with his W. Make sure you get level 2 as fast as possible to deny him the level 2 all-in.
Once Maokai has his E, he can place his Saplings E in nearby bushes and zone you away from them. Make sure you stand at the opposite side of the lane so the Saplings E can not damage you.