Let me think.
Give me a second./ Give me a minute. / Let me think for a second.
比如对方问了你个问题，你可以说 Give me a second. I need to think about it.（给我一秒钟，我得想想。）
Give me a minute. I need to think about it.
Let me see.让我想想
A：Where did I put my keys? 我把钥匙放哪儿了？
B：Let me see. I think they might be on the table. 让我想想。我觉得它们可能在桌子上。
How should I put this.
How should I put this? It's difficult for me to find the exact words to describe it. 我该怎么说呢？我很难找到准确的词来形容
To be frank...
To be frank, I haven't thought about that yet.坦率地说，我还没想过那个。
Hang on a moment.
Hang on a moment, I'm trying to recall the details.等一下，我在努力回想细节。
Believe it or not
Believe it or not, I saw a shooting star last night. 信不信由你，我昨晚看到了一颗流星。
I mean
I mean, it's not that easy to solve this problem. 我的意思是，解决这个问题没那么容易。
As a matter of fact
As a matter of fact, I have been to that place before. 事实上，我以前去过那个地方。
To be honest
To be honest, I'm a little bit nervous about this presentation. 说实话，我对这次演讲有点紧张。
Let me recall. 让我回忆回忆，适用于要回忆事情的场景