Distinguishing between plot and theme is the most basic things. Plot refers to events while theme refers to what the author is trying to convey. To distinguish between the two and learning the art to make a difference, one has to read the story thoroughly from start to end a couple of times. Once you are done reading, take a notepad, and write a single line that summarised the entire story. After you have written the sentence, think about the themes. Jot down as many as you can.
Read the story yet again, and underline or highlight all the nouns that the writer has used frequently to describe about something special.
Now elaborate the inherent connotations of all the nouns you have just highlighted or underlined in the story. For example if you were reading ‘The Alchemist’, the author has used the word ‘Treasure’ several times. With the word ‘Treasure’, there is an image of gold, jewellery and such other things come into one’s mind. However, if you think hard, then you realise that the author has not used this word in this context. Its actual meaning is something else. Try to jot down whatever comes to your mind, and repeat this process with every other noun as well.
Once you have jotted down all the meanings that you have considered that the author has used in the story, try reading the story once again, and try to replace all those words with the one’s you believe they represent. If any of them fall apart, then think again what the author wants to convey with that noun. Once you have determined what that word or noun actually represent, it means that you have started to identify symbols in literature.