Be happy; sleep well. A normal person who wants to have better focus and memory, such as for work or school, can do some simple things. Get healthy (get rid of aches, pains, stiffness, and tummy gurgling). Avoid "mild" drugs like caffeine, nicotine, alcohol, or over-the-counter sedating or stimulating medicines. Sleep enough and properly (same daily schedule). Maintain a happy mood (avoid anxiety, fear, sadness, etc.).
Brain fitness. Recent advances have shown that many cognitive functions can be enhanced and developed by use and exercise. There are programs and ways of exercising these skills that improve memory and focus. A hot topic of research now.