Capable people get asked to do more. That is a compliment until it becomes a problem. The answer is not to say no to everything but to say no clearly and kindly to the right things.
Phrases to borrow
- I can do this, and it means X moves to next week. Which matters more?
- I am not the best person for this, but Y might be.
- Not this month. Can we look at it again on the first?
- I want to do this well, so I need to say no for now.
Notice that none of them apologise. A clear no is a form of respect for the person asking.
