如果有人求你帮忙，但你实在无法帮ta，那么试试这么说：

I'd like to help you but I can't take on any new commitments at the moment, I'm afraid.

我很想帮助你，但现在恐怕无法再增加任何新任务了。

给予Ta信心，鼓励Ta独立完成

Actually, I think this is something you could do really well yourself!

事实上，我觉得您完全可以自己做好！

Why not have a go yourself, and give me a shout if you need help?

要不您先自己做着，在需要帮助时喊我？

打时间牌

I need to think it over.Can I get back to you later?

我得好好考虑一下。我稍后告诉你好吗？

I'll think about it and let you know, OK?

让我考虑一下，然后再告诉你，可以吗？

“嫁祸”他人

I'm afraid I'm not familiar with that, but have you asked (X)?

我对这个事情不是很熟诶，你问过某某了吗？

Sorry, but that's not really something I can do. Maybe (X) can help you.

抱歉，我实在做不来这事。也许某某可帮你。

Oh dear, I'm terrible at that sort of thing!What about getting (X) to have a look at it?

哦，亲爱的，我最不擅长做这种事情了！让某某来看一下怎么样？

总之要记得，不要急于回答“是”或“不”然后再后悔。考虑清楚后再回答，保持礼貌但要坚决，而且确保让事情朝自己希望的方向发展。