1. watch tutorials on youtube and learn the basic principles of tactical shooters - crosshair placement, movement, positioning, utility usage, map knowledge
2. develop game sense by playing a lot. you can do this by playing unrated or competitive games, but i recommend doing deathmatches as they are the best way of getting into gunfights quickly
3. communicate with your team! it doesn't matter if you have the shittiest aim in the world, your team will still appreciate your comms. in a tactical shooter communication is crucial, especially in ranked games.