You need to know what relaxation feels like, first, then work it into your daily life.

So first, you need a space and time for complete relaxation, a bonafide daily-ritual that you can do which separates the 'hustle and work' part of your day from your 'relaxed and calm' part. This ritual will eventually cue your subconscious and conscious mind to shift gears into a (more) relaxed state.

I'll use my daily-ritual as an example.

As soon as I come home from work I take a shower and make some coffee (this is part of the ritual, in which my thoughts of the day are transitioning towards more mundane things), then I put on my relaxation clothes, something loose-fitting and comfy, which for me is a sarong and a big cotton shirt, then I make myself a mug of coffee and go to my balcony, where I sit in my comfortable chair and assume a relaxed position. I play some soft music on low as a background to the sound of traffic, and watch the sky turn into a canvas of color as the sun sets, all the while, I consciously refrain from thinking of anything negative (that shitty interaction I had today, the upcoming expenses I have to pay, that looming dead-line I have to meet...etc.) Instead, I think of things like the self-esteem-boosting fact that I've made it this far in life, or reflect on a pleasant memory from my past, or how cute that girl on the bus looked when she giggled, or simply how beautiful the sky is. You get my drift.

An hour of that and I'm relaxed enough to enjoy the things I want to do afterword, whether it's fixing dinner or watching a show or getting on the playstation.

Find that place and time and make a ritual for yourself. It can be the neighborhood park, or the roof of your building, or a cozy cafe nearby, just as long as its somewhere you can watch the world go by from a detached viewpoint while relaxed and unharried. Perhaps meditate, or listen to music on your headphones, or just people watch, or even mindlessly daydream about the future while strolling around your (or a nicer) neighborhood.

Do this for a while and that relaxed state of mind will begin to seep into your life, if you let it.