What is the best way for me to improve my health to become more productive?

Hi, I'm 27. I feel pretty unproductive often. A lot of the time, I'm hot and/or tired and can't focus very well, and feel slightly sluggish and below equilibrium. Which of the following is most likely causing this?

1) I smoke weed a lot

2) high caffeine intake

3) lack of exercise

4) relatively unhealthy diet

Which of these has the biggest impact on my everyday energy levels?

What is the best way for me to improve my health to become more productive?
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