Know the game secrets: like some easter eggs, and at least all the basic mechanics
Have a good equip/level/idk, it depends on the game you are playing. Many players say that they are pro just because they have some rare objects, but that is not true, to be a pro you have to have all the requirements in this list
Know some tricks: It is useful to know while you are speedrunning in minecraft that you have to stay 3 blocks high to kill an iron golem, you don't think so?
Be good at the game, and know that there is nothing bad if someone is better than you,
Have fun: this is the most important one if you want to be pro 😎