LPT: mentally designate a space for each of your cards in your wallet and make a habit to put them back in the same place immediately every time.

This accomplishes two things: 1. It gets you into the habit of putting your cards away immediately instead of putting them on the counter, in your pocket, etc. where they can get lost. 2. If something does happen to your card, you will notice immediately and will have fewer steps to retrace to find it again.