It's grammatically correct, but "intensify" is probably not the best choice for a verb to communicate your thought. And we usually collocate "positive" with "energy" is this context. I would suggest: Do things that fill you with positive energy. If something fills you with positive energy, do it more often.

Yes, it's correct. "Intensify" is an unusual word choice. It may be a perfect word choice, depending on what you really mean. "Intensify" as you have used it means "do it with more intensity," which is different from "do it more often" or "do it longer." Suppose you run every Sunday, you run 4.5 kilometers, and it takes you 30 minutes. If that fills you with good energy, you could "intensify" that by still spending 30 minutes, still doing it once a week, but running faster and achieving 5 kilometers in 30 minutes.

Hi Hamid The sentence is correct as it is. A more natural sounding sentence might read: Focus on all things that fill you with good energy. Hope this helps.