A team is not five good players. It is five players who keep showing up to the same plan. The captain's job is the second part.
A roster is a schedule, not a group chat
The first real decision a team makes is a night and a time. Lock it. The squad that knows when it plays will outlast the squad that is always "trying to get five on."
Run a real match night
Warm up together, agree on a default for each map, and assign roles before you queue. Ten minutes of structure saves you three thrown rounds.
Stop saying you should make a team. Pick a night.
Review without blame
After a loss, the captain sets the tone. Name the mistake, not the person, and move to the fix. Teams that can review calmly improve weekly. Teams that argue dissolve.