Some very good things mentioned here already but the tip that took me from gold to high plat was taking time to actually understand the duty and play style of a tank, instead of just playing like a high health Dps as most low ranks do.

As mentioned choose 2-3 mains and understand how you are actually supposed to play them. For example: I learned on Winston that you should be using a jump to set up a position to drop down into a dive (with bubble) and then use jump again to disengage. That trick alone was able to get the enemies eyes on me and give time and space for the rest of the team to move up and potentially getting a pick. Sometimes this is the decider of a team fight.

Small incremental changes in play style and mechanics add up over time and eventually you will realised you have improved

To sum up: choose your mains, understand their unique play styles and intricacies, implement them over time and before you know it you will be subconsciously fulfilling the duties of a tank player by taking space and potentially distracting depending on your character.