The easiest change that is likely to improve cognitive performance is in the area of diet. In particular, a proper ratio of omega 3 to omega 6 fatty acids in the diet is needed for proper cortical brain function. While these benefits have been proven in clinical trials only in young children - incidentally likely accounting for part of the 7 IQ point advantage of breastfeeding, which has also been proven - they likely apply to adults as well.The ideal ratio of omega 3s to omega 6s is about 1:1 or 1:2. These days, most people get most of their dietary fat from vegetable oils which have an unbalanced ratio in the range of 1:20 or 1:30. Getting rid of the vegetable oils in favor of animal fat from pastured animals is ideal. Failing that, getting some omega 3s from fatty fish, the best source, can partially offset the poor fatty acid balance of vegetable oils.For people older than the onset of metabolic syndrome, typically in the 40s, excessive blood sugar levels and swings tends to become an issue. A reduction in dietary carbohydrate intake - less sugar and starch - can help avoid this issue. There may be some additional benefit to going to a ketogenic diet, which provides an alternative source of energy to the brain - ketones instead of glucose - especially as ketones provide more usable energy per unit of oxygen.The next easiest change is exercise. For older adults - again, roughly those of us past the onset of metabolic syndrome - exercise is useful, probably because it helps burn off excessive blood sugar levels and stores. Anaerobic exercise is especially effective since it burns blood sugar less efficiently, and thus uses more of it.Then, there are changes in intellectual habits. In particular, it’s likely worthwhile to do a lot of reading. This is partly because reading builds vocabulary, which contributes to most peoples’ definition of intelligence and also is an element in many IQ tests. In addition, though, critical reading - thinking about what is read and its implications - helps one practice logical and rational analysis. Don’t worry about reading things that you think are good for you, just read what you enjoy enough to think about analytically. Find quiet, undisturbed time to do your reading.Learning math through calculus is probably also useful. Math at these levels - arithmetic through algebra to calculus - is applicable to all sorts of everyday issues. Do you have enough money to make it through payday? Arithmetic. What combination of potluck dishes do you need to make sure everyone has enough main course and dessert at that party? Algebra. Can you make it through the yellow light before it turns red? Calculus. I’m not saying you should break out the pencil and paper and write down equations for all these things, but if you’ve fully learned the math, you should be able to apply the concepts to these and many other everyday problems, even if your goal is not an exact numerical answer.Edit: Finally, there are other people. The more time you spend in the company of people smarter than you are - but not so much smarter you can’t understand them - the more opportunity you have to learn things from them, including thinking habits. Perhaps this one should have been first.Don’t expect an overnight change. Even babies take years to demonstrate the benefits from that initial year of breastfeeding. Keep up the good habits year after year, though, and you’ll likely see some benefits.