dbdmaps.com has good explanations on the tiles, maps and gen placement. Not sure if they're up to date with the latest changes but it should be a good read.
Generally for nearly every gen or also totem, they are somewhat evenly distributed around the map. The generators are placed so that they usually are a few tiles away from another although there are often pairs closer to each other. For example a corner gen and one only a bit further towards the map.
One or two gens are usually in the middle of the map.
The picture I posted is too symmetrical, but you can see the basic idea. Most setups will be similar to this with only for example B being closer to A or C or something similar on the other parts of the map. You can basically split the map in the middle and there should be 3 on each side and 1 in the middle.
It takes a bit to get used to the setups, but after some games you'll get to know where the gens usually hang around. Until you get them down you can just look for the lights, they are good to spot in open maps.
Indoor maps are a bit different. For example on Memorial Institute you can look for the neon signs - if they glow, there is a gen in that room. The game has those large doors that only open when the gen is finished. So if you see one of those closed, there is a gen at the door.
If you really want to scout the maps out, you could also play custom games on your own as killer so you can immediately see where the gens are.
Vanish builds are so fun! Watching the confused killer circle around the tile from a locker is great.
Head On for defensive or Lucky Break for more bamboozling also fit in the 4th slot.
My version of this was Lithe+Dance with me and do a slow jump into the locker on the next tile or around the corner.