Try this exercise from Temple University:
Once a day, watch 5 cars go by, and make a mental note of the colors, in order. After the fifth car passes, distract yourself for 30 seconds. Then, try to remember the sequence of colors. Once you can list 5 colors in a row, work up to six, seven or eight. Then you can start adding details, like the type of car….Say, black SUV, white pickup, red sports car….Do this once a day, and after a month, it’ll boost your memory by about 20%.