Regular daily physical exercise A healthy diet: for example the MIND diet: low in fat and sugar, high in vegetables and fruits, regular hydration. Be mentally active Participate in social activities Get adequate sleep (7-8 hrs nightly) Manage stress Limit alcohol/avoid smoking Periodic medi...

The same that is needed for preventative general health, there are no evidence-based lifestyle measures unique to cognitive impairment.  Here is a fact sheet with citations from the Physicians Committee For Responsible Medicine.