Installing discipline especially after a period of indiscipline is a big work but not impossible.
The first thing is that you the dispenser of justice has to have proven beyond all criticisms that you have a reasonable level of discipline.
Always be the one not to do what should not be done.
Correct in love.
Before you correct an erring member openly, let it be that you have corrrected the person secretly.
Correct mistakes and don't go personal.
Punishment should be reasonable and consistent with indiscipline.
Do not be partial or differential in measuring discipline.
Maintain your stand even when majority differ in opinion.
And pray for tranquility.