Get enough sleep and avoid stress. Without sleep you can't concentrate, and if you are stressed you can't think straight. Try exercising your brain by learning a language, knitting or playing computer games. A study of 200 people in Minnesota aged 70 to 89 found those who had been mentally active in their 50s had considerably better memories. Eat healthily – participants in memory competitions swear by oily fish. Lay off the booze.