This isn’t easy nor is it hard. Like anything you have a choice in your heart and mind whether you want to accept that feeling, incident, experience or not. This includes skeletons from your past and things not yet occured in your future.
To do this you have to reduce mental noise, all the bullshit that clouds your head. Doing this isnt easy but may i suggest a book called the power of now, and a film called the peaceful warrior, to give you insight. Further, you need to develop an intrinsic or inside out approach to life. That is first be, then do and achieve. What I mean by this is that doing/buying/verb things won’t bring you happiness, this can be sourced from the book the happiness trap. You find your not happy or sad but rather just placid, at ease and peaceful.
What I have found is that once you learn to be present it doesnt stay that way. You have to always be in tune with your mind and body, and adjust accordingly when events occur that bring you back to old habits.