Challenge 1: Questions
In questions, the subject is often either after the verb or between parts of the verb phrase.
Where are my slippers?
Will we be going to the mall?
We will be going to the mall.
Challenge 2: Commands
In commands, the subject of the verb is always the unstated you.
Raise your hand. = (You) Raise your hand.
Challenge 3: Inverted order
Sometimes for emphasis, writers will switch around the parts of the sentence. In those sentences, the subject is usually after the verb.
Behind the bookcase is the door to the secret room.
What is? The door is.
The door to the secret room is behind the bookcase.
Challenge 4: Sentences that begin with here/there
If a sentence begins with here or there, here or there is never the subject.
Here are your missing earrings.
There goes the four o'clock train.
What are here? Earrings.
Your missing earrings are here. (In this case, here works as an adverb.)
What goes there? Train.
The four o'clock train goes there. (In this case, there is an explicative expression.)
Challenge 5: Subjects followed by prepositional phrases
Sometimes a noun is followed by a prepositional phrase explaining more about the noun. It is easy to confuse the subject with the object of the preposition.
The box of books belongs in the library.
The members of the committee worked hard to come up with a plan.
The box (of books) belongs in the library.
The members (of the committee) worked hard to come up with a plan.