Where to start is put the modem/router in the middle of your home if possible and check the signal in various places in your home and go from there..
If you have a wiring-panel where the modem 'needs' to go, consider getting your own router to put in the middle of the home, otherwise look at access points to connect in a couple places that already has network cable run.
There are a LOT of options and ways go get this done. Don't know until some sort of site-survey is done on your home, which is usually easier after getting service, but it can be done before depending on what you have around.