“Sally and I” is grammatically correct when it is placed before the verb and is the subject of the sentence.
“Sally and me ” is only correct when “Sally and me” are the objects of the sentence.
Sally and I are going to the cinema.
The most important thing to remember is that “I” is the subject pronoun(the person that does the action) and “me” is the object pronoun(the person that receives the action. You can read more about subject and object pronouns here.
When “Sally and me” is incorrect
“Sally and me” is incorrect at the beginning of the sentence because we do not use “me” as the subject of the sentence.
People tend to make this mistake as the subject includes more than one noun but more commonly with a name such as John or Sally.
We are so used to subject(I) + verb that this structure is disrupted, it can be easy to make a mistake.
I remember being corrected as a child that it is always “my friends and I “ and finding it difficult to say this structure.
I play tennis.
Subject verb object
She loves me
Sally and I play tennis
When to use “Sally and Me ”
“Me” is an object pronoun that means that you receive the action. “
Peter punched me.
In this example, you received the punch. It doesn’t make sense to say “me punch”.
You can only use “Sally and me ” when you and the other person(Sally) receive the action.
They started a fight with Sally and me.
The artist painted a picture of Sally and me.
It is just a form of politeness to put “Sally” before “me”.