I am nice.  I am not nice.  I am going to be nice.
You are my friend.  You are not my friend.  You are going to be my friend.
He is very tall.  He is not very tall.  He is going to be very tall.
She is at school.  She is not at school.  She is going to be at school tomorrow.
We are the champions.  We are not the champions.  We are going to be the champions next year.
You are in my History class.  You are not in my History class.  You are going to be in my History class next semester.
They are in town.  They are not in town.  They are going to be in town next month.

Sujeto + to be + complemento (generalmente in adjetivo)
Mary        is        pretty.
Sujeto + to be + not + complemento.
Mary        is      not      pretty.
Sujeto + to be + going to be + complemento.
Mary        is       going to be      pretty.

Espero te sirva!