Remove all bedding, rags, leaves, debris, anything that hides them and/or makes them comfortable.
Screen off the foundation 100%. Between the house and the patio, and the patio and the outdoors, seal all edges, cracks, and holes with electrician's putty or concrete. Pay particular attention to plumbing, HVAC, and electrical ins and outs.
Fill larger voids with Great Stuff Window & Door, aka the more expensive Great Stuff. The cheaper version degrades in UV light and moisture. Mice can chew through GS but it is tamper evident. The purpose is to seal off attractive smells and temperatures (warm air exfiltration in Winter, cool air in Summer).
Seal cracks with silicone. Mice can chew through silicone, the purpose is to block the attraction of smells and more temperate air. Also it is evident where they are trying to get in and out if you find the silicone chewed-on. But for larger cracks and accesses, seal off with electrician's putty or concrete.
Use a combination of rat-sized sticky traps with peanut butter, and poisoned bait (pets allowing). Leave traps inside and outside the screen.