Saplings can be tossed into brush for empowered effect - but don't stack well.
Try looking for flanks or other situations where Nature's Grasp is unavoidable or takes enemies by surprise.
Maokai's passive makes him extremely durable against focus fire from spells - so long as he can still basic attack something.
Saplings will chase the first enemy that gets too close, but detonate after a few seconds or if they collide with other enemies. Be especially careful around brush sapling, as they are much more dangerous.
The cooldown on Maokai's self healing is heavily gated on how many time you hit him with spells. Careful about wasting abilities on him.
Maokai will avoid taking damage while he's using Twisted Advance, so don't waste your spells.