There’s a word you can use to change the tone of a lot of situations, and that word is 先(first, xian1).  You can use it in a lot of situations to soften your tone.  Contrast the stark and brusk nature of 别(contraction of 不要) with the tender and mild nature of 先不要.  Take a look at the sentences below to get an idea:

你别走 – Don’t leave!
你先不要走 – Oh, don’t leave yet! (stick around; stay a while)

There’s another use of 先 which is important to know about, which you can see below:

我们先走了 – Well, ok, I guess we’re going to get going.
我们走了 – [flatly] We’re leaving (now).

Now that you have these, people will be pleased at your ability to soften your speech!