What is happiness is a question too hard to answer. However manifesting happiness in one's life can be taken up in baby steps. I have never thought of myself a happy or an unhappy person as I think things are not quite black and white like that. What I have done over the past few years, specially since starting to work for myself is however to keep my mindset in check, at all times possible.
When you spend the most of your day by yourself and you are your own employee and employer, it is very easy to for your whole life to be taken over work. In my case, work is something that makes me happy. I wake up in the morning wanting to work and I have hard time leaving my desk in the evening if I haven't completed my to-do list. I have come to a position where my productivity of the day has become a strong variable of how happy I am on that day. While this may be logical at first as one's career is important and especially when you are so passionate about your work, you do put in a lot of yourself, both intellectually and emotionally.
However, I have recently asked myself the question what if I couldn't finish the last task of the day? Is that really going to change my level of happiness? If so, why? have I allowed a simple tool like a to-do list to decide how fulfilled I am on a specific day. Then I realised that at some point in this journey of working hard I have let the tools manage myself instead of me managing the tools and as a result of that, feeling happy or disappointed has become a result of an output of the system I created for myself.
So, now I am learning to let go and compromise. Being a perfectionist doesn't really help me very much here, but I allow myself a bit of free time and if there is a task to two left undone at the end of the day, I don't burn the mid night oil or loose any sleep over it. I ask myself every morning, what are the tasks that has to be done now, so that tomorrow will exist and if there is anything that is not urgent and important, I leave the to be done at the end of the day. Sounds simple, yet the key is in the mentality of being able to let go of the perfection, and I have found a lot of happiness in letting go. I find myself relaxing towards the end of the day and I generally have more time to spend with friends and family.
Quite paradoxically so, the quality of my work also has improved (according to my audience) despite of my lack of perfection and less amount of total number of working hours and that has made me more happier than ever!