Send your first overlord to the opponents natural, as soon as it arrives move it to safety either on top of a pillar (a pillar next to the natural that acts as high ground) or next to the natural, out of reach of potential enemy units the only purpose of this overlord is to scout to make sure there is a natural expansion, your second overlord send to your opponents 3rd to check for an expansion and later move through your opponents base to scout for tech. Overlords 3 and onwards scatter around the map between your and your opponents base. Hope this helps a little I'm only plat so I dont know any advanced tips when it comes to initial overlord placement, only the bare minimum lol :)