How do I put this? vs. How shall I put it?
When I talk to someone and want to stop to find proper words to express something more clearly, I usually say, "How do I put this?" and then go on.
I used to think that "How do/shall/can I put it/this?" mean pretty much the same thing, but I've found recently that "How shall I put it" tends to be used if you're going to say something that may sound rude.

Is that true? How should I use these phrases then?

Question

How do I put this? vs. How shall I put it?
When I talk to someone and want to stop to find proper words to express something more clearly, I usually say, "How do I put this?" and then go on.
I used to think that "How do/shall/can I put it/this?" mean pretty much the same thing, but I've found recently that "How shall I put it" tends to be used if you're going to say something that may sound rude.

Is that true? How should I use these phrases then?

Answer

I would say "How can I put this?...hmmm.."   because you are looking for a possible way to say something gently.

"How do I put this?" means there is a normal way to do it...  I don't think that's really true, and..

"How shall I .."  means "How will I.."  ("shall" really isn't common except in the south of England, in my experience - most people think it's funny/posh) like you are thinking/trying to decide.   That means you are telling the person "I'm trying to trick you by finding a way to say something bad, gently!"  ha ha

Answer

"how do I put this" should suffice if you really have no idea how to express that thought, and "how shall I put it" is perfectly a good sentence to be used when you think you are going to say something that is honest but may sound rude, For example: "How shall I put it?/let me put it this way, he’s rich, but he’s certainly not attractive". but I am not a native speaker so let's wait for the opinions of native English speaker.