Enjoying Life in the Present?

You know how you'll look back and think "oh, those were good times then...if only I had known it at the time..."? I was thinking about that today as I went out to play tennis, and I thought to myself, what does it take to truly live in the moment and enjoy it? I feel like I always have some doubt, some inhibition, in the back of my mind, something holding me back from truly living life happily. I don't know what it takes to live in the moment. Maybe it's to just let go and to let yourself be happy. Sometimes you do need to force yourself to be happy, I realize this.
As I walked out to the courts I noticed my surroundings. There I was, playing tennis. I wasn't that good, but I was getting better all the time. Under the shady trees with the cool autumn breeze and temperatures rolling in, life was beautiful. Autumn had arrived and taken over the summer. We have no say, but this change was welcome to me. Summer slipped away before my eyes. So my life will do the same if I don't take some action to make life mean something. There I stood looking out at the quiet suburban streets. Life was alright. It wasn't as bad as I was always making it seem. My life was and is not perfect, and it never will be. I need to accept this, and let myself live as well as I possibly can in every moment. I don't want my life to be one big regret of all the hate I felt, all the happiness I deprived myself of, and I won't let it end up that way.