My team had an offsite a few weeks ago, and there was an exercise about goals. The most common answer is about happiness. Our little team offsite cohort is a good representation of us all. We all want to be happier, and it’s our life goal to be happier.
Much has been said about how to be happier. Comfort food, pet my dog, or go for a run. Logical adjustment of expectations balances the equation of happiness = reality - expectations. These are things I do when I'm feeling low, to brighten the mood. But I wouldn't necessarily call them the path to be happier, or to become a happier person.
Here's my theory about happiness: To be happier is a long-term effort, often when we don't feel the need to be happier.
Happiness is a moving curve with peaks and valleys (really happy or unhappy). It's more than normal to have mood changes, and over time everyone establishes their baseline, let's say call it the baseline happiness.
Food and comfort can get us up from the valley, but it's almost guaranteed that our mood will change, and the cycle starts again. Psychologists Philip Brickman and Donald T. Campbell call this the hedonic treadmill. It is called a "treadmill" because, like running on a treadmill, it feels like moving (experiencing ups and downs), but you tend to end up in the same place happiness-wise. 
Since we want to be happier, it's actually less about how we feel at every moment. To be happier, it's less about what we can do now to change how we feel, but rather to improve our baseline.
To move the average line up is to change how we "generally feel" when life is not at the peak or valley. To move the average line up, the traditional method of having comfort food or calling somebody to vent may not work. It moves our mood, but not necessarily our baseline.
There are definitely ways to move up our baseline. But we usually want to 'be happier' when we are at the peak or valley. At the peak, we want to feel like this forever. In the valley, we never want to feel like this again. Let's call them Moments of Reflection.
The funny thing about happier is only 10% of life is at the Moments of Reflection, but only in these moments we would consciously want to take action on "to be happier". 
When the highs and lows pass, we get along with life and forget about the reflections and effort needed. That's what makes it so difficult - we have the 90% of life to work on it, but barely do.
To be happier, is to constantly work on our happiness when we feel ‘normal’. Everyone has their journey, and there are a few things that worked for me.
Relationship
Having more healthy Relationships is the most obvious way to increase the baseline for me. It means to deepen the relationship with my wife, my parents, my dog, and my close friends. I also found that investing in my relationships (money and time) provides disproportionate returns - no matter how much I put in, I always become a little happier.
The simplest way to invest in relationships is to do more for other people. Pay more attention, plan more, and always show up.
Do Hard Stuff
Doing hard stuff created spaces when things didn't go our way so we can soften the blow. It translates to different things for different people. Work hard when it's not the time to relax, so none of the work seems difficult. Exercise hard as if it's a matter of life and death, and all other physical hardship is easier to endure. Push yourself to get uncomfortable (like asking Starbucks for a discount) so rejections and life accidents surprise less.
One additional benefit is appreciation becomes more obvious, and being grateful becomes easier to do.
Anticipation
Having things to look forward to works wonders for me. It can be as small as a planned weekend, vacation next year, or waiting to see a friend's reaction for a customized birthday gift. When I was doing annual planning earlier this year, life felt quite hopeless because of grief. But this sense of loss disappeared almost instantly when we set a goal to buy a house this year. It's quite magical - the anxiety, or the thing in my stomach, simply disappeared when the anticipation of buying a house materialized.
In the end, the journey to becoming happier is a continuous process, not a destination. It's about making small, consistent efforts during those 90% "normal" moments of life, rather than seeking drastic changes during emotional peaks or valleys.
Remember, the goal isn't to eliminate these fluctuations but to create a more resilient and content version of ourselves that can better navigate life's ebbs and flows.
Wish you to become happier, and enjoy each downhill and climb back up.