English is easy: it's what you know about a text, and how you know it. As for showing how you know it, I recommend the STEEL model: STATE your position; name a TECHNIQUE being used; provide EVIDENCE from the text of that technique being used; describe its EFFECT on the audience; and LINK it back to your statement.
If you are struggling with language forms and features (techniques), then I strongly recommend you get your hands on a copy of "Edible English" (the author's name escapes me), if you do not have one already. It's practically a bible of just about every conceivable language technique you are likely (and unlikely) to encounter.
Make sure you substantiate everything you say with evidence from the text. There's nothing that frustrates me more than an essay where a student points out something recurring through a text, and then provides a single example of it.
Don't approach your work from a purely narrative standpoint. If you are studying a film, be sure to mention filmic techniques; similarly, if you are studying a poem, then be sure to mention poetic techniques. Likewise, don't just recount the plot of a text. If I set a text, chances are that I already know the plot. I am looking for you to demonstrate the meaning that you get from it, and show me how you got it.
Your assessment tasks should come with a marking criteria. Don't just disregard it. Those criteria are how your assessments will be marked. Sometimes it might be difficult to distinguish what each means - ie, there is a difference between "demonstrates detailed knowledge" and "demonstrates thorough knowledge", even if it is not immediately apparent - but if you get stumped, ask your teacher. Those criteria are set by the faculty, and are written with your outcomes (the things you should be able to do by the end of the course) in mind. If your teacher cannot explain them, go to the head teacher.