Hello! You can help a lot of people if you write a great paper about a topic that is important for teaching English. The first step is to get excited about your project, and that should be easy since you are entering such an important and interesting professional field.
You have to choose a topic based on what is happening right now in the field of applied linguistics for teaching English. A discussion is taking place in the form of all these articles that people write about the topic. I searched Google Scholar for this: applied linguistics, teaching esl
Now I can open several articles that are only 1 or 2 years old. Scholarly articles usually have a review of literature, and of course your paper will have one, too. The review of literature is like a review of everything that happened in the discussion. You review everything that has been 'said' in the discussion (i.e. review the articles that have been written about applied linguistics for teaching esl). Only when you have reviewed the things that other people said in the conversation are you qualified to participate in the conversation.
So, the way to choose a topic is simple: Read some articles that interest you, and start to write your Lit Review by writing about the other things people have been saying. Soon, you will be enjoying the process of reading the most advanced, recent research findings in this professional field you have chosen. You will want to enter the conversation, because you will have something to say.
After reviewing the recent literature you'll know how to plan a research project that logically builds on the findings of some other recent research project, or you might notice some important questions that have not been answered in recent research.
By reading several recent articles that interest you and choosing a topic that you can use to make a great, interesting contribution to improve the way English is taught, you'll be establishing yourself as a real authority in your professional field -- someone who knows the most up-to-date research findings and what they mean in the context of the ongoing discussion among linguists and English teachers.