Going from low-mid diamond to master

Last year i played really stubborn and the main reason i even climbed was because of my duo, i feel like my actual level of play was around plat 3 and i was toxic. This year im not only reformed but my champ pool is good and i feel like im winning lane allmost every game. The main problem for me is making a difference, since i am a support main at the end of the day with lacking mechanics, but what i consider to be a good knowladge of the game. with champs like braum however i can sometimes struggle to win lane by pure decisionmaking, because of not being on the same page as my adc. im stuck in d4 rn and im confident ill be getting d3 soon judging from the skill difference between me and opponents, However what is actually the difference between a d3 support and a master support? Id really like tips from anyone, because i feel really motivated to hit masters ( just like my old duo bud) and play together again. (If there are any coaches interested that dont ask insane prices im allways up)