I see so much advice that tells you to say yes to everything.
No. I am too picky for that. I am too busy for that.
BUT - I have learned to say “Why not?” and answer it seriously. Useful answers include: Because I don’t want to. Because there are things I care about more that it would displace. Because I need time for me. Because it does not reflect the person I want to be.
Less useful answers are the usual litany of: I won’t get accepted anyway. It seems good from here, but what if I don’t like it? I don’t think I can finish it.
For further growth, try: What would have to change about it to make it a yes? Closer to home, on a different weekend, pays better, better working environment, when I have more time, maybe if I knew more about it, whatever. This is great practice in helping you recognize the things you DO want to do sooner when they come up.