Running ethernet cable from living room (main floor) to second floor office
As others have said without seeing you house there is no way to answer this question exactly. Some techniques that might be useful.

You have an unfinished basement (this is a great start as it allows you to move horizontally below the ground floor.

You don't mention it but you probably have a loft space that allows you to move horizontally above the 2nd floor. When you find the right wall simply drill a hole in the top plate and drop a weighted string down and you can pull a cable.

In terms of vertical runs look for where existing utilities already run the length of the house. Think air conditioning ducts, toilets, plumbing etc. I'm not suggesting you run in the ducts/pipe but there is often a space beside the duct/pipe you can use.


Something you fill find useful,

fish tape (ridged metal tape you can use to push/pull something at a distance)
weight and string (for dropping into cavities).

Ultimately it comes down to exploring the options in your house.