our previous 1s captain picked who he wanted with no regard for who/how many that left to go into the 2s & 3s. He also failed to check properly that all those selected for the 1s were actually available in the first place, leading to several incidents of nabbing 2s players on the morning of the game, the knock on effect being the 3s would be left short with not enough time to find replacements. This, I think, led to a certain degree of animosity between the teams.
When taking over the job I decided to personally ensure we always had enough every week, and then pick teams jointly with 2s captain. We are fortunate in that the 3s captain is happy to have whatever team we've picked for him, but he knows we make the effort to ensure his team isnt absurdly weak (not always possible).
If anyone drops out they tell me, and I find a replacement, or ensure one is found. It saves tooing and froing between captains, lots of people asking around then finding we've got too many, or asking the same person twice etc....
Not an ideal system, but we dont have the luxury of a vast squad, so we cant really say to people "if you dont tell us by Tuesday, you havent got a game" because we'd end up cancelling half our 3s games!
(An indication of what a struggle this years been for players is that our 2s skipper has played more in the 1s than the 2s this year...)