It's just like exercise. Do some every day, even if it's only a little bit. Eventually, you WILL see results. It's not usually anything mind-blowing, but one day you just notice better stamina, or better concentration, or some other thing like that. And the more you do, the more it will grow. It does kind of snowball, in my experience (both the physical exercise and the mental), but you often can't see "big results" immediately. That doesn't mean there aren't results, or that they won't compound as you continue.