Encourage your child to play games like Chess. Every game of Chess is different from the previous game. This teaches your child to look at any problem from various angles, and to learn that there can be numerous approaches towards following a problem. On the other hand, skill games require you to perform the same steps at the exact same time, throwing you into a mental rut and narrowing your approach to problem solving. Thus your brains become naturally more flexible with strategy games.
Also, such games of strategy encourage thinking and exercise those brain cells. Your child's problem solving abilities and critical reasoning skills will get sharpened. Similarly, solving puzzles and quizzes will sharpen your child's brain and will keep him alert. Memory games will, as expected, improve your child's memory. On the whole, games that require your child to think will improve your child's mental skills far more than simple skill games, which focus more on hand to eye coordination.
It is imperative that your child gets a minimum of eight hours of sleep a day to boost his brain power. After a day of studies, your child needs a good night's sleep to ensure what he has learnt stays rooted in his brains. The next morning, he should re-revise it. Extensive research shows that when you sleep less, you weaken your powers of recall.
Similarly, after school your child should make it a point to revise what he has learnt. If he only studies last minute, chances are that he remembers little of what was taught in class. But if he comes home and revises his classwork even for a very short time, he will register it for longer.
Cutting down salt from your child's food can also speed up your child's powers of recall, especially if your child is overdosing on sodium intake. A teaspoon of salt per day should be all a child needs to take in per day. If your child has more salt than this, you should cut it down. Remember that all tastes are acquired. If you put your child on a low salt diet from the outset, he will stick to eating foods low in salt - at least for a while. And later on, in adult life when he decides he needs to cut back on salt, he will find it easier to do so.
Make sure the water your child is drinking is pure. Water needs to be boiled and filtered before it is drunk, so make sure you do so. Drinking water with traces of aluminum can cause the brain to deteriorate over the years. If you live in a country where it is safe to drink tap water, in any case attach a filter to the tap to remove all traces of aluminum. Also, avoid wrapping food in tin foils. It is not bad for health, but it is possible that it causes damage over an extended period of time.