Olaf doesn’t have the healthiest clear early. If you have strong duelling potential: somewhat equal to Olafs, you should look to invade him and try to kill him while he is low.
He has good Dragon control thanks to his Passive and Q. Make sure you take the bottom side Scuttle Crab and keep the Drake warded so you can spot him in case he tries to take it.
Olaf is going to be looking to gank often in the early game. Having vision around the river and jungle entrances will reduce his ability to get successful ganks off.
In team fights, Olaf will look to isolate and take down the highest-value target using his R. Ensure that the strongest members of your team cannot be engaged on by positioning safely.
Olaf loses both armour and magic resistance when he activates his Ultimate R. If possible, focus him while he is in his more vulnerable state before he can deal damage.
When no team fights are occurring and when no objectives are up, Olaf may stick to a side lane and start to split push. If you can, try to use the numbers advantage to start a team fight while he’s unable to assist his team.
Once Olaf hits level 6, it will be difficult for you to kill him or lock him down with CC. Don’t commit to using any hard CC abilities when you know his Ultimate R is up.
Olaf is a skirmish heavy Jungler and will be looking to gank frequently in the early game to get himself and his allies ahead.
Olaf can solo objectives in the early game with ease. If there are no gank opportunities for him, he may be trying to take the Dragon instead. Keep it warded at all times so you can see him on it.