Rats can squeeze through a small hole. It’s a genuinely unsettling fact. So one of the most important things you can do is walk around your home, really slowly, with a torch if needed, and look for gaps around pipes, cracks in the foundation, spaces under doors, loose vents. Steel wool is great for stuffing into holes because rats can’t chew through it. Then seal over it with caulk or expanding foam. It’s not glamorous work, but once you’ve blocked their entry points, you’ve solved a huge part of the problem.
In the garden, raised beds with a wire mesh bottom discourage burrowing. Dense low ground cover like ivy can be a favorite hiding spot, so clearing some of it out near the house helps too.