Tip: Admit it is your fault. That is the only way to actually improve. You can continue blaming your team if you choose, but you will not climb that way.
Subconsciously you know that it is only you who can make you climb, and your team doesn't matter which is why you are here asking for tips anyways.
Once you are to the admittance stage, just review your games, find your mistakes and fix them. Also you can have better players review your games if they are willing so that you can hear the mistakes you make that you may not even know are mistakes due to current level.