The highest I got soloQ was immortal 2 before they completely revamped the ranking system.

I quit playing for a few months and now am back grinding again and have only managed to hit diamond 2 so far.
It seems pretty clear that immortal 2-3 is not what it was 6-9 months ago and is much harder.
I am looking to really grind and get better at this game so I want to ask for those who are high immortal or radiant, what are things that you do that make you so highly ranked?
If you could pick a few things, what would they be? Are they things you practice on a consistent basis?

Also if you don't mind, please also list the agent you play as well!