Assess how to respond to a sentence. If you can say "yes, I will do that" or "no, I will not", then it is an imperative sentence. An imperative sentence gives a command. "There is a key in the door" is not imperative because you cannot respond with "yes, I will." The sentence, "Turn the key in the door" is imperative because you can logically say "yes, I will do that."
Look for heightened feelings in the sentence. The exclamation point (!) is a key sign of heightened feelings, so its presence is a good indicator of whether the sentence is exclamatory. "Turn the key in the door!" is exclamatory, as is "Did you turn the key in the door?!"
Consider if a sentence is either both exclamatory and imperative, one of them, or neither. This is important because it proves that sentences don't have to only have one type.