Brain development

[Dovahkiin]

Most of your brain develops in early childhood by various processes, Though most important aspect of higher intelligence is based upon genes, But proper nutrition and good amount of sleep is very important in young brain development. Now as I understand your question was about cognitive abilities, Genetic parts can't be changed But nutrition (dry fruits are very good for brain development and functioning as they are good source of essential fatty acids) also Proteins are required for good memory along with sufficient sleep (transfer of short term memory into long term memory happens through protein transcription in brain, and protein transcription can only occur during sleep).

Brain trains itself for many important things doing apparently menial tasks, If you like what you do, You would obviously have easier time concentrating. For cognitive functions and decision making, Playing video games helps a lot but it would be more in general manner and it depends upon you how to take advantage of that in real life. Somehow I am of opinion that meditation just help in relaxing and doesn't work in development of brain or any particular cognitive function. Life experiences also help you in understanding world around you and decision making.

In Today's era of technology one needs boss type of memory and not that of a Secretary, remember important things, have a basic knowledge of things you are interested in and patience to learn them in details when need arise. In my experience, concentration is based upon task at hand, If you like it You will have better concentration, if you don't then you won't have it, obviously there could be some exercises which increases concentration but I never tried that. I let my brain develop doing things It liked to do.

These are all my personal experiences, experts in field might have different opinion.