Best CS:GO Tip?

As Red said, Crosshair placement absolutely is a number one priority. The second thing is positioning, game sense, and those are just things you learn through playing the game.

However, my biggest tip, is to have fun. There are too many toxic players and don't be afraid to mute them and lose a game. You're playing to have fun and you get better over time, everyone has a shitty game, and eventually there will be some guy seemingly at an airport that is always dead spectating you to let you know what you did wrong after you've done it.