Play a deck that is meta with a high win rate. I know cards can be an issue but if you can build quest shaman, it's insanely strong. If you can't climb at lower ranks, your choices are not optimal or your not anticipating what your opponent can play. Here is a good resource for decks https://www.hearthstonetopdecks.com/decks/.
I would recommend watching a streamers video and pause it each card and determine what you would play then resume the video and see if you choose the same. If not think about what your choice was weak too and why they choose that card over your selection. Being knowledgeable about what is meta and what your opponents win conditions and threats are is a solid way to increase win rate. Best of luck keep at it!