All writers feel like they're stuck sometimes.
It can be confusion about what you should write next that stops you from putting down the next word. Or it can be an unwillingness to focus, to concentrate, to get started. It could be a feeling that whatever you write will be crap, so why bother? Or that it's too hard. It could also be resentment that it's required. Or it could just be that you have other stuff you'd much rather do and that's distracting you.
Let's go through those issues:
1. Confusion about what's next. If you have an outline, follow it exactly. If you don't have an outline, write one. Outlines really work as ladders to help you climb through the writing process so you don't get stuck in figuring out the next step. Follow the essay format.
Also, if you can't figure out the next sentence, think about imagery -- often, describing something with your senses will help you move forward.
Another possibility is to skip the difficult choice for now and write a different section. There's no rule that says you must write the essay in order. If you're stuck on Reason 1, write the Conclusion . . . and go back to Reason 1 later.
2. Don't want to write. Sometimes the act of writing, especially the idea of sitting down and getting started, feels loathsome and repulsive. The first step to fixing that is sitting down and writing something, anything, just to get the language flowing. You can always delete this "throat-clearing" later.
Switch up your method. If you usually write in a notebook, write directly on your computer or your phone. Or if you always write on your laptop, try pen on paper.
Sometimes it also helps to change your environment. Go someplace else where nobody is bothering you and there's a calm atmosphere. Often the action of choosing a new or different location to write helps put you in the mindspace to get work done.
You might also want to switch up your music, or have some comfort food. Caffeine helps, too.
3. It's going to be crap. Yeah, it probably will. So what? You can fix it later. In a first draft particularly, don't let perfectionism, fear, or your internal editor stop you from writing words. Allow yourself to be awful at first. Who cares? You're not chiseling this essay onto a marble headstone -- you're writing on paper or in a word processor, and everything can be changed easily.
Don't worry about grammar or spelling or generalizations or generics or whatever other rules you have in your head. Those can all be revised. You have to check for that stuff afterward anyway, so don't worry about it up front. Blurt out your first attempt just to fill up the pages.
4. Writing is too hard. Yes, writing is very difficult. It's hard for everyone. Don't throw yourself a pity party about it. Language is slippery, and it's tricky to reach for what you want to say and find the best, clearest way to express your ideas.
But you can do it. You are better at writing than you think. Center yourself and write what you know, think, and feel, in your own words. Your writing is valid and worthwhile. Your voice is necessary in this world. Other people need to read your work because your exact experience is unlike anyone else's.
Write like you're talking, telling a story, explaining to someone -- a friend, parent, sibling, teacher, boss, priest, child, significant other -- your ideas. Sometimes it helps to actually talk through your essay with someone. Explaining it out loud will help focus your thoughts into words.
Don't get fancy or give yourself extra difficulties in the language. It helps me to repeat a line of Gertrude Stein's: Sometimes the best way to say it is just to say it.
5. I have to write, so I don't want to. Yeah, I'm a rebel too. Nothing is fun if it's required. Then it's work, right? Then it's a chore. So how can you make it fun? How can you make writing feel like play? Enjoying yourself while writing will make it enjoyable for the reader, too. Make sure you care about your subject, that you're genuinely curious about what you're writing -- that will help you stay engaged. Be funny, be smart and silly, get stylish and cool. Put on a stupid hat or a ridiculous outfit and shake your shoulders to upbeat music as you write. Let go of the resentment, and get it done.
You can also reward yourself with a treat for getting a specific amount of writing done: If I finish Reason 2, I can play Xbox for an hour. Beware of rewarding yourself with cookies, though! That's how I got fat.
6. There are a million things I'd rather do . . . or that I have to do. Certainly it isn't always easy to find the time to sit down and write. It helps to have a set routine for when you work. You can't wait until you feel inspired. It's so easy to procrastinate and find other tasks. My kitchen is never cleaner than when I'm on a deadline. But when you catch yourself doing something other than writing your essay, ask yourself, Is this necessary right now? If it is, then finish it up. But if not . . . admit that you're distracted. Get back to writing. Sit in the chair and write some words.
Use a timer. Set a countdown for 20 minutes and get that clock ticking. During that time, don't allow yourself to do anything else but write.
If you can't write at that moment, do the next best thing -- research your subject. Sometimes reading other people's ideas will help motivate you to argue with your own. But stick to researching your essay! Don't let yourself go down the wrong rabbit hole.
I hope some of those ideas help you get unstuck and plow through the first draft.
Remember: the best trick to get writing done . . . is doing some writing.