Where to ward

It also depends on the different stages in the game, how far into a lane you are pushed/pushing. If you are under your tower, you are less likely to need a river ward. Top vs bottom lane, playing top vs playing bottom can also impact where you place.

I agree with what has been previously said. Your vision should be defensively placed in the sense of watching for ganks. You do not necessarily require anything more than your trinket ward early on.