Well I was a daily heroin user for a few years. Now I chip (went full circle you might say back to how I started).
Basically my living situation had just become untenable to me. Personally I found the emotional attachment harder to deal with than the physical dependency. I had started to lean on the drug to basically prop me up because I was very maladjusted. Plus simple habituation is an incredibly powerful driver purely because the brain likes routines, and does not like changing them. Everytime you perform a certain behaviour you strengthen neural connections to do with that behaviour, which in turn facilitates more of it, until you're stuck in a mindless self - reinforcing loop.
For me it was re-discovering old interests, plus adding a couple new ones, which helped the most breaking me out of the habit. Things to enjoy and fill my life with. I'd basically forgotten how to do anything except do drugs and get drunk, so needed to re-direct myself.
What I want to make absolutely clear is that I'm NOT talking about 'distraction' or 'replacement'.
I believe this to be INCREDIBLY counter - productive and self - defeating. The reason being, if you're thinking in those terms you're keeping your focus on the substance instead of genuinely directing it somewhere else.
If you need to 'distract' yourself, then your reference is still the drug, and if your distraction fails you'll blame yourself. If you're 'replacing', then that's a tacit admittance you're engaging in a substitute activity for which your only motivation is that somehow it's supposed to prevent you from doing the thing you REALLY wanna be doing.
So the best advice I can give is this :
First, be absolutely clear on why you want to cut down. Speaking from personal experience, 'because I just should / owe it to my family' is too vague and doesn't keep you going for long.
Secondly, when looking for things to get into, DON'T copy others. Someone might tell you 'oh I never touched xyz since I started exercising' , or the like. Then you start doing exercise but still find yourself at your DOC all the damn time and wondering why the magic power of exercise (or whatever else the other person took up they claim 'made them stop') doesn't do the trick for you. Humans are individuals, not copy - pastes.
Whatever you choose has to be individually and personally meaningful FOR YOU. That's why I can't recommend you any specific activity. The important thing is that you should find it fulfilling and enjoyable IN AND OF ITSELF. I don't for instance climb up mountains with my camera so that I don't chase gear all day long instead, I do it because I want to be doing that very thing. It's not a case of 'better make myself do Z otherwise I' ll end up doing F', and that's a crucial difference. What are your interests, what might you always have thought of trying out but never got round to -? And ideally it should be an activity that's incidentally incompatible with being high, for obvious reasons. Sorry to disappoint if you were hoping for a precise step - by - step instruction on how to change a habit, but that's never how it works.