Everyone gets anxious about something. Most people are anxious about things they either don’t have much experience in or have struggled with in the past. Maybe you are out of practice with writing, or maybe you did poorly in a previous English class. Even though writing is often graded and evaluated using certain guidelines, writing in itself is a very individual process. Writing is just another form of communicating with others, and everyone does this in their own unique way.
Do you find it easy to express your thoughts verbally? If so, see if you can transfer those verbal thoughts onto paper. Consider getting a tape recorder and vocalizing your thoughts, then listening to a recording and transcribing it. You might discover that writing is easier than you thought. Even if you do not consider yourself a strong conversationalist, think of some other areas of strength for you. See if you can incorporate some of these strengths into your writing. Are you good at coming up with ideas, organizing them, explaining them in simple terms, writing concisely, summarizing, or researching? Do what you are strongest in and get support in areas that you might struggle with.
Pushing through the anxiety and getting the job done (whether it is writing a paper, taking an essay exam, or writing a college application statement) will make you feel more accomplished, more confident, and more capable.