Check your tires daily with the gauge of a floor pump. You'll figure out how often you need to inflate assuming your ride length is in a narrow range. I commute 28 miles a day and know that inflating every other day works well. I always pump after metric century day and if I haven't ridden for a couple of days. I have 25c (which measure 27mm when inflated) at 100 psi.

It's really not that big a deal to check at home with a floor pump. Don't forget to check tires for slices and cuts, too!