First, let me define an intentional life. Being intentional means you are doing something on purpose. When you make an intentional decision, you are deciding that you are doing it. You take control of what you are doing which leads to a better life. An intentional life is being aware of your day and deciding you are going to make certain choices.
I believe the awareness that intentionality uncovers is a key factor in leading a happier life. When you are aware of things in your life, you have more control over how you take on your day. For a surface level example, I am aware that next week I have three exams and that this weekend I really want to make a road trip to Nashville. Three ways I can approach this. One, don't go on the road trip and be studious all weekend. Two, go on the road trip and deal with the stress later. Three, realize that I have four days to study, set aside time for each subject each day to study, go on the road trip and allow that time to de-stress and not think about school, and then review the day before when I get back. Now which one of those seems like the most intentional approach?
Becoming aware of what I have to do and what my priorities allow me to be intentional in what decisions I will make next. This shows how awareness and intentionality connect. Now for a deeper example, I can be a very impatient person. I like to get things done quickly and do multiple things at a time, so when something is taking longer than expected or I need to focus on only one thing, I become very frustrated. However, becoming self-aware of my impatient tendencies has helped reduce this frustration. Knowing that there are certain things that require more time and energy helps me go into projects with that expectation. I know this, therefore, I can choose not to let frustration get the best of me. I can make the intentional decision to take my time and take a break when annoyances are arising. Being aware and choosing this route reduces so many negative aspects of getting things done.
I challenge you to try this approach. Take some time to reflect on some tendencies that you need to work on (it's okay we all have them). Whatever they are, become more aware of them. Then once the opportunity that challenges those tendencies arises, make the intentional decision to detect it and make the better choice. If you find yourself judging people easily, take a second and pray for them instead. If you find yourself being hostile towards a person and they approach you, choose to listen. If you do this over time, I guarantee you will be happier because progress correlates with happiness.