To optimize broadband signal, it's a good idea to connect your router to the telephone master socket or fibre router, that's usually the one closest to where the telephone line or fibre enters the building and the termination box is placed. This becomes more important if you have a low quality line.
To optimize wireless signal, you should try and find a location that's around the centre of the building, not tucked away in a corner (or in close proximity to walls, radiators or electrical appliances), and raised off the floor.
There's no one-size-fits-all rule for this, so try placing your router in different locations and see what works best for you.