how can i improve my posture?

[Joey]

So lately ive been getting a lot of crap about my posture, and that im really hunched over and I look like a primitive human. I remember my posture started getting bad in 6th grade(im a senior in hs) but now I have to admit even I think its pretty bad. Like now my shoulder blades are merged with my back so u can hardly feel or see them, my arms/shoulders now naturally go toward the front of my body and my shoulders look really hunched. It really annoys me to look at, but everytime I try pinching my shoulders together they go back after a few minutes unless I hold them back but usually without even noticing I will relieve pressure and they will slowly go back to the way they were. I try walking with my shoulders back but I always forget and when I forget I naturally go back to hunching. How can I improve my posture, thanks.