Guide to English grammar

5 The imperative with a subject
We can mention the subject you when it contrasts with another person.
I'll wait here. You go round the back.

A practical guide to English grammar 21

You can also make an order emphatic or even aggressive.
You be careful what you're saying.

NOTE

1. 
   A few other phrases can be the subject.
   

All of you sit down! Everyone stop what you're doing.

2. 
   The negative don't comes before the subject.
   

Don't you talk to me like that. (GB)

6 Let
1 “Let's (= let us) + base form of the verb” expresses a suggestion.

It's a lovely day. Let's sit outside.
Let's have some coffee (, shall we?).

Let's suggests an action by the speaker and the hearer. “Let's sit outside” means that we should sit outside. The negative is let's not or don't let's, and for emphasis we use do let's.

Negative Emphatic

Let's not waste any time./Don't let's waste any time. Do let's get started. We've wasted enough time already.

NOTE
The long form is formal and old-fashioned.

Let us give thanks to God.

For American usage, • 303(3).

2 Let me means that the speaker is telling him/herself what to do.
Let me think. Where did I put the letter?
Let me see what's in my diary.
Let me explain.
Let me think means “I'm going to think./Give me time to think.”

NOTE
Let can also have the meaning 'allow'.

Oh, you've got some photos. Let me see. (May I see?)

3 After let we can put a phrase with a noun.