While all situations are different, in our 2 story home with an attic it was very simple.
The Blue Iris computer is upstairs in a guest bedroom closet where there was an existing Ethernet keystone and 110v outlet. The main POE switch is in my wife’s walk-in closet where there is a recessed structured wiring can. So, yes, the two hardest areas were already wired and I was lucky.
For the cameras, Ethernet cords leave the structured wiring can and go into the attic. Then some are routed to the top of the office closet which is your standard 2 door one. We installed PVC pipe in the closet in the corner nearest the doors so it would be hard to see unless you stooped and turned to see it. This pipe went to the garage ceiling where a few Ethernet runs went directly to outdoor cameras and one run connects to another POE switch which supplies runs to other cameras and an access point. The hole in the garage ceiling was caulked with fireproof caulking for fire and CO infiltration to the upstairs office closet.
The Ethernet runs are stapled to the garage ceiling and exit the walls of the garage where I wanted a camera to be installed.
Two of the out door cameras had to be fished but it only took the Low Voltage installer about 30 minutes. The hardest run was to get a wire from the attic down the wall in our bedroom then through the floor and to the outside of the wall. The solution was to use this corner molding, which blends into the corner because it is painted the same color as our bedroom interior walls:
The cameras have since been replaced with Dahua turrets.
The black tray holds a UPS and the silver thing is a UniFi 8x150 POE switch. You can see to the left of the UPS where the pipe enters the garage from the attic.
Like others have posted, get a quote from an electrician. They are amazing at fishing wires.