People watch. Go down to the beach or a pedestrians only street in your area (in L.A. 3rd Street Promenade is good or a street in Beverly Hills that has a lot of foot traffic), and get a latte or a cup of tea and park yourself at an outdoor table.
Watch people as they pass. Try to guess what kind of work they do, where they’re from, where they’re going. See if you can imagine what their lives might be like. See how much you can notice about each person. Do you see details? What color their clothes are? What kind of shoes they’re wearing?
After you’ve done this for about an hour, take your tablet (real paper is good but you can use your laptop or iPad if you want) and see if you can write down lots of details about the people you saw.
This process not only sharpens your memory skills without feeling like work, but you feel like you’ve been to a cocktail party and met a lot of new people!