Remember that those categories don't actually represent skill, they just represent wins. Win more, get promoted.
Now, if you're asking "what can I do to improve to make myself able to beat diamond players", that's a different question and philosophy entirely, more akin to the other answers in this thread, surely there are many ways you can improve mechanically and strategically.
But there will always be people in higher leagues than you, who have worse strategy and mechanics. They aren't better than you, they just won more and lost less.