When you receive a writing assignment topic, it is a good idea to start brainstorming by listing main ideas or key concepts as a desk work. Then just jot notes by them. There is lot of methodologies to list out the topics. Many people in common put circles around each thought and join them by arrows. This process may lead to a longer article.
Decide on the type of paper you are writing. This may be assigned by your teacher, but you may have to give an opinion and justify the opinion. Keep in mind the correct subjects and verbs to use.

Start researching your topic: Make sure you know what your teacher will and will not let you use on your topic and assignment.
Start with the most general source first, so you can learn about the topic then work your way out to the most specialized sources. Use print materials. Before you use internet materials, make certain you know what is allowed for your assignments

Generating parameter for selected topic: You do not want to be too generalized or too specialized. Make sure you pick a topic where you can find enough information.
Make a summary of your information. It may help to take this to your teacher, so you will know if you are on the right track. If it is necessary to write out your opinion or your thoughts on a topic, make sure that you have the facts to back it. Always remember to be a critical thinker and keep an open mind.