“Read, read, read. Read everything -- trash, classics, good and bad, and see how they do it. Just like a carpenter who works as an apprentice and studies the master. Read! You'll absorb it. Then write. If it's good, you'll find out. If it's not, throw it out of the window.”
—William Faulkner, Nobel Laureaute in Literature
Sadly, there is no way to completely remove all the difficulty nor all the anxiety from a process such as writing. But that is probably as it should be. After all, we always feel anxiety before a test, a competition, or some other event about which we care a great deal.
Hopefully, though, the process outlined above will make writing much easier and less momentus (or mountainous) for you.
The other thing that will help you feel more confident when approaching a writing task in English is simply doing it over and over. The more you do anything--with conscientious effort, of course (which means attentive revision!)--the better you get at it.
Also, READING a great deal, not only in the field you plan to write in but other areas as well (e.g., for PLEASURE), will improve your facility with English and the written word.
In any case, good luck in your quest to become a better, more effective, and less anxious writer. And above all:
—E. Grunwald, 3/31/16