"You can't improve everything at once," she continues. What's more, if you do manage to incorporate multiple interventions at once, you don't know which intervention actually helped. "What I recommend, since I'm only talking about 15 minutes a day, is to just pick a single mental target that you're trying to improve, a main intervention that you're trying to work on," Ricker says. For example, let's say you want to focus on creativity—keep this mental ability in mind as you move along to the next rung.

https://www.mindbodygreen.com/articles/neurohackers-plan-to-upgrade-your-brain-in-15-minutes-day