Hi to both pjf1215 and rowan_willow.
Have more confidence in yourselves! I wonder if you're thinking the problem is bigger than what it actually is. Start with small steps, and you can build on those.
Step One : make sure you're really familiar with the texts you're reading. No substitute for that. If you don't know them, you can't proceed.
Step Two : when you're given a title/topic to address, unpick the wording of it so that you end up with a clear and simple statement of what it is it's asking you to discuss. Once you've got something specific in your mind, it becomes easier to address. Coupled with text knowledge, you'll be able to think of particular parts of the text, relevant quotations and references, and maybe even similarities to other texts.
Step Three : Plan how you're going to take on the essay title. An A3 sheet of plain paper could be where you write down everything that you think you want to use. When you've done that, go back through your ideas, which should be accompanied by references and quotations, and see if you can group them into categories - eg character, theme - and colour-code them with a highlighter pen.
Step Four : This is where you start to raise your grade. Once you've done Steps 1-3, you've probably covered the obvious stuff, which gives you the basis for properly interrogating your text, through the lens of your title. Don't stick only with what you've covered in class. A higher-grade student will think independently, and question authorial intention etc. Remember, English Literature is a great subject to study because it gives you so many opportunities to have a different viewpoint (as long as you can reasonably support it with evidence from the text).
What I've said here is pretty general guidance. It would be helpful if I knew what texts you were studying, to see if I can suggest something more focused.
At the end of it all, though, I would suggest that - if you haven't done so already - ask your teacher. To say your responses are not suggestive of 'thinking big enough', or are 'too vague' is fairly vague in itself.
Anyway, think about what I've said. It seems basic, but maybe it will focus your thinking?