Skills increase over time with practice. As a student you will notice this especially acutely when it comes to your ability to write essays. This is a natural consequence of your vocabulary expanding along with your knowledge base. The thing that may continue to be difficult for quite some time is the expressing of your opinion in an academic context. If that has always been something of a challenge for you, try this out:
Your essay will be bland and unconvincing if you are not sure what you feel about the particular topic you were given. If it is something you regularly think about it will not be hard at all to put your words together but if it is a matter that never crosses your mind or affects you this can be troublesome. Spend some time in deep thought and see what emerges.
Once you know what you believe in this case, consider the view points that are most different from it. There may be several so feel free to list as many as come to mind.
Having come up with all of these alternative theories, you will need to think and research until you have found a reason why they are not true. If you cannot do this then you have discovered a flaw in your logic and perhaps your original opinion was wrong. This requires you to critically analyze all of the dissenting views in order to discover the truth. If you only do it half way so that you can preserve your impression of yourself as correct, your essay will suffer. You will need to find a way to adequately argue your original view.
Having hashed out the other aspects of this paper you will need to put it all together in draft form. The result should appear very much like a complete essay. It will simply need to be polished a bit so that it is ready for proofreading, editing and then finally submission.
This process will d wonders for you but only if you use it regularly. Make sure that the essays that you are assigned by a teacher are not the only ones you ever work on. Consistent practice is the key.