Sleep
Remove distractions
Remove or reduce sugar and alcohol
Sun exposure in the morning
Caffeine a bit later and none in the afternoon
Meditate to practice getting back to the thing you want to focus on, eg a breath, once you got distracted
And supplements? Maybe D3, and, anything else, likely best only if to know from blood work that you have a deficiency, assuming you eat a balanced diet with all need nutrients
Otherwise, yeah, magnesium, etc.
Or ephedrine for a strong, potentially unsafe and illegal kick, but I'd use it in emergency only, not a sustainable thing