Don't go near the bushes in the the top lane if you notice that Maokai has thrown a Sapling in one of them as they will chase and blow you up if you walk by them
Be aware of ganks. Maokai might be weak in a 1v1 setting, but he is great in small skirmishes and he has a decent gank setup. Keep the lane even and the river warded at all times.
When playing as a skirmish heavy laner, opt for early magic resistance items to protect you against Maokai’s dueling potential as he does dish out a lot of damage thanks to his Sunfire Cape.
His only hits a single target per bramble. Stay in a line and let your tank take the root from it. Also don't run from it if you know you wont make it out. The root duration is longer the further it travels.
Maokai is great at scouting vision with his Saplings . When moving around the map, do not walk directly into bushes. Instead, walk to the side and play cautiously when close. If no Sapling is present, continue forward.
Maokai will stick with his team while his Teleport is down. Try to abuse this by splitting up and taking down towers in the side lane. If Maokai tries to stop you from pushing- duel him.
On his first back, Maokai will most likely pick up a Bami's Cinder and look for skirmishes with his new found power. Play accordingly and be prepared for a more duelistic gameplay.
Once Maokai has completed his Spirit Visage, he will gain a lot of health regeneration. Make sure you invest into a Grievous Wounds item to reduce his healing.
When Maokai gets Righteous Glory, make sure you stick together and do not split to far apart. Splitting up my allow Maokai to use its active and take down the isolated target.