let's not (do something)

When you want to suggest that people in a group not do something, you can say "let's not ___". For example:

Let's not go out tonight.

You can use "Let's not ___" when you're suggesting something that you're sure the listener will agree with. In the example above, you think that everyone will agree that it's a good idea not to cook.

It's also common to say "Let's not..." when you're someone with authority, like a boss, or if you feel very confident in sharing your suggestions and decisions. In these cases, you can use this phrase:

Let's do that, OK?

Let's not spend too much time obsessing over the details. We have a lot of other things to talk about.

not bother (doing something)

The phrase "not bother ___ing" means to not do something that isn't needed. For example:

Don't bother washing those — I'll put them in the dish washer later.

I don't bother shaving on the weekend unless I have to go out to meet with someone.