How do I make sure my essays are always structured well?

There are three ingredients you need when writing and structuring any English lit essay:

Introduction 

PEE

Conclusion

In every essay you need an introduction to your essay, usually about the theme or character you are writing about and a conclusion at the end summing up the arguments you have made. In yor conclusion and introduction mak sure you refer back to the question you are answering. 

In each paragraph throughout your essay, you just need to remember PEE.

POINT- this is the point you are making about the character or theme in your book. Maybe you are saying that Lenny in Of Mice and Men doesn't know his own strength. 

EVIDENCE- this is evidence from the text to support the point you made. This might be a quote or just highlighting a point in the text that shows when Lenny didn't know his own strength. 

EXPLAIN- Having evidence is important, but you must explain why it is relevant to the point you were making? and how does it link back to the question you are answering?

If you can remember this basic cheat sheet in any English lit essay then it will be structured well.