I have a Prusa i3v 10" printer that I have had quite a while and have most things dialed in and working well with it...
Except, sizing.
Doesnt matter if its something I design or downloaded online.
For example, if I print something that is supposed to have a 608 bearing pressed into it, i will have to sand the hole larger for the bearing to fit.
Or, if its a design that has several 3D printed parts that will fit together, they will never fit together and require sanding and cutting.

What are the main things I should be trying in order to fix this?
Thanks