You never know...

"You never know" means that there's a small chance that something could happen. Use this to talk about something that probably won't happen, but is still possible.

A common way to use "You never know..." is to say that something might be useful in the future. For example:

A: Do you want to keep this? We don't use it anymore. 

B: Yeah, let's keep it. You never know...

You can also use it when you're hopeful that something great will happen:

I like to dress nicely, even if I'm just going to the grocery store. You never know – I might meet the man of my dreams there!

Well

There are many reasons to use "Well" at the beginning of a sentence. One reason is to defend yourself.

When someone has attacked your actions or something that you said, you can say "Well" before you explain yourself:

A: You never do the dishes!

B: Well, that's because I don't use as many dishes as you.

A: You broke it!

B: Well you're the one who told me to hold it like that!

Defending yourself with "Well" can make you sound a little childish when you use it in an argument. But you can also use "Well" to defend yourself a little more calmly:

A: Don't you have to go to work soon?

B: Well, yeah, but it's OK if I get to the office a little late.