1. I do not have that time free in my calendar. I really appreciate that you invited me.
2. I have so much on my list right now that I simply cannot take on more.
3. Sorry, I am not able to say yes to that request. Thank you anyway.
4. I cannot commit to that right now; however, I know someone who may be interested.
5. Unfortunately, it is not a good time right now.
6. That sounds interesting however I am swamped at home. Maybe another time.
7. I am not comfortable doing that task. Do you mind asking someone else with more experience?
8. The timing is not good right now. Keep me in mind for next time.
9. Perhaps you can try on your own first and come to me if you get stuck.
10. Thank you for thinking of me. However, I need to finish this priority project before I take on anything else.