Against olaf, 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 t. 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. Against olaf, Olaf doesn't have the healthy light early. If you have a strong duel potential: a little equal to Olafs, you should look to invade him and try to kill him while he is weak. He has good Dragon control thanks to his passive and t. Make sure to take the lower side Crab Scuttle and keep the Drake guarded so you can spot him in case he tries to take it. Olaf will look for gank often in early play. Having a vision around the river and jungle entrances will reduce his ability to get successful ganks.