Drills
The session goal and the score
In one line: Five minutes in total: one goal written before playing and a score from one to five at the end.
Goal
Give every play session a direction. Without a goal you just play; with a goal, even an evening of losses leaves you something.
How to do it
Before you start playing, write a single sentence: the habit or drill you are working on today ("I check the minimap after every kill", "I always go in with a teammate"). You can take it from the habits or the drills.
At the end of the session, before closing the game, give yourself a score from one to five on that goal alone. Not on results, not on rank. Write the score next to the sentence and keep it for next time.
How you know it works
It works when, after two weeks, your scores on the same goal have gone up. At that point the habit has become automatic: pick another one. If the scores do not go up, the goal was probably too broad: make it more precise.