The "wir" imperative
There is also a "wir" form of the imperative which equates to "Let's do something" rather than being an order. Just like the "Sie" form of the imperative, you merely take the normal "wir" form of the present tense verb and follow it with the pronoun, which cannot be omitted. Any separable prefix will come at the end of the clause.
"Gehen wir!" (= "Let's go!")
"Spielen wir!" (= "Let's play!")
"Lesen wir!" (= "Let's read!")
"Fangen wir jetzt an!" (= "Let's start now!")
The imperative forms of "sein"
The verb "to be" shows irregularity in the imperative in that all of its forms use "sei-" as a stem. This means that the "wir" and "Sie" forms of the imperative are different from the present tense forms of the verb.
"Sei glücklich!" (= "Be happy!")
"Seien wir optimistisch!" (= "Let's be optimistic!")
"Seid pünktlich!" (= "Be punctual!")
"Seien Sie glücklich!" (= "Be happy!")