Let’s + infinitive without to is often used to make suggestions. It is rather like a first-person plural imperative.

    Let’s have a drink. ( = I think we should have a drink.)
    Let’s go home, shall we?

There are two possible negatives, with Let’s not . . . and Don’t let’s . . .

    Let’s not get angry. Don’t let’s get angry.
    Let’s not is considered more ‘correct’.