At the core of every sentence is a subject that contains at least a noun or pronoun (the pronoun standing in for the noun). This subject does the action of the main verb:
A noun can also be the direct object of the verb. In other words, it receives the action of the verb:
Emily ran a marathon.
If the noun is the indirect recipient of the action, then we call it the indirect object:
I sent an email to Madeleine.
A noun can also be the object of a preposition:
The wind whispered through the trees.
There are other uses as well, but the point is that nouns don’t exist in a vacuum. They have a job to do.
And that’s what will allow you to recognize the more confusing nouns, especially the ones that are more abstract or look like actions. Take the following example:
Practice took a long time.
The word practice might look like an action, and in another sentence it might be a verb (I practice), but here we already have a main verb (took). So we can figure out that practice has to be the subject (the thing that took a long time), and only a noun or pronoun can be the subject.