This is a really good question. For a long time, I kept waiting hoping to get better so I could be "happy" again. But somewhere along the way, for me I figured that happiness wasn't a destination, it was part of the journey.
I made a concerted effort to find "happiness" in my day-to-day existence. I noticed I was happy when I was watching my puppy play; when I tried a new recipe and it turned out good and my family enjoyed it; when I heard a favorite song; when the fresh snow fell and the trees had sparkles on the limbs; etc. I learned to catch myself being happy and then proceeded to do more of the things I enjoyed and to enjoy more things in my day-to-day life.
No, there is nothing happy about some of the traumas I have suffered or in some relationships. Frankly, I've dumped those relationships and the traumas are in the past and the current traumatic events I have no control over. (My daughter and I were both diagnosed with cancer in the past 18 months.) But I have learned to find happiness and to be happier, by living in the present and finding it throughout my day. Don't get me wrong, I still get sad, anxious, fearful, etc. but that is not my state 24/7.
Other things that I do to help is to cut out as many negatives as I have control over. Stay away from the news, listen to music you enjoy, light candles that smell good, treat yourself to a mani/pedi, play with a pet, go for a walk and enjoy nature. Squeeze out as much happiness, joy, peace, laughter, etc. from each moment in the day that you can. At first you have to look for it, but then when you find it, you can find more of it.
This isn't anything a therapist taught me. It came from realizing there are certain things I have no control over and I cannot change. It just something I have learned to do as I didn't want to have any more moments of my life robbed by my past. I can control my perception and I just decided to slow down, notice, and increase the number of things that make me happy throughout the day.
Just my .02.