Hi, long time player - full time noob.
I've been playing this game super casually for years now, occasionally dabbling in ranked and hitting silver 5 as my highest. How on Runeterra do you set up for a dragon? That's something I've never been able to figure out.
Others may have better answers, but a simple answer would be to make sure you have vision in the areas surrounding the dragon pit, as well as clearing enemy vision in and nearby the pit. For example, if I'm blue side, I like having vision near the enemy blue buff, bot lane, mid lane, and the corridor between blue buff and mid lane. That way you can see anyone coming and prepare for it.
Beyond vision, a good time to do dragon is when 1 or more enemies are dead, or you know they have multiple members top lane or far away without teleport.
