When is Enough Too Much

This question has been on my mind a lot lately. I think about it when I am at church, at school, or at chorus. When have you volunteered for too much? How do you stop yourself? If anyone has the answer to the last question I would really like to know the answer. I keep thinking that I will stop and focus on maybe one thing at a time. I think school, church and chorus are not too much but volunteering to teach, sing, be in leadership, etc. can be too much because I am not a focused person. I really want to plan but then I think what if they need me at church or what if we have something at chorus I can help with. Yeah, I plan around what other may or may not need me to do. Hopefully, with some prayer and reflection I will get this all figured out.