I try using my diaphragm but I cannot breathe properly

ashfittis

Still I think it’s the smoking my breathing is terrible I use the diaphragm but still really hard to use

Furious_Phil

It is actually pretty tricky to get used to... I liken it unto when I first did some snorkeling. At first my breathing was panicked and irregular when my head was submerged; but once I relaxed into it, I was able to level out my breathing and enjoy the experience.

Diaphragmatic support (to me) is a little like Chi Kung or yoga breathing, where you do a very slow release exhale from your diaphragm for an extended period of time. The trick is to not panic and gulp air into your lungs, but to keep everything at an even keel.
Like just about everything, this takes practice.

PS - You are correct in that your smoking is greatly reducing the efficiency of all of it.