Just trying to point out that if you see 1 mouse you have more. First step is to keep more from getting in.
I spent quite a bit of time a couple of years ago trying to do just that. Unbeknownst to me, behind the stove in the kitchen there was a small hole in the wall that led right into the space between the studs. I really think that they were getting in by crawling behind the siding and finding that hole. I plugged it with copper mesh and foam-based sealant. I don't expect to see too many more mice inside ... knock on wood!