Writing can be done differently between people so make sure you understand that not everything in this list will help you write or help you get started. The easiest things to do are often the most simple and overlooked methods that I have found help me immensely when I am struggling with writer's block.
Look back at the text.
I know your teachers and parents probably tell you to do this all the time but often starting with the text is the most important step because if you don't understand what you are writing about then it will be very difficult for you to do it. Also, this can provide more details that you might have missed like finding a topic or finding facts that can support a chosen or given topic.
Pick a topic or a stance.
If you are not already given a topic or a side to be on (the stance) then you will probably struggle with your writing assignment. Most of the time if you are dealing with a class assignment then you are given a rough outline of the idea and this could help you find your topic or stance however for most it is not that simple. If you are just free writing then finding a topic to write on can be more of a hardship. The way I usually overcome that is to just start writing whatever comes to your mind until something resonates with you.
Something else that can help you find a topic or just overcome your writer's block is to sit down and find something that inspires you. Things that usually work for me are song lyrics, so if you also enjoy music then try sitting down and listening to some song and try and really hear the lyrics! Another thing I usually find helpful are YouTube videos. Especially, the fan-made videos or the multi-fandom videos that are set to music or have quotes from the shows or books or movies, because those are things I can remember to add to my own writing.
Talk to some of your friends or people you respect their opinions.
One of the easiest ways to get help is to ask for it. So if you are struggling with finding a start to your writing or you are stuck not knowing where to go next, just talk to a friend or someone you trust. Just getting someone else's input or outside perspective can help you more than anything else can because you get the chance to get out of your own head and relax because you are not alone anymore!
Take a break!
No, this does not mean you get to procrastinate that will only stress you out more!
What this does mean is that if you have been struggling for longer than an hour and you are not under the extreme time crunch of needing to have it written in the next few hours or so then just stop trying for a few minutes and give yourself time to rest and relax. If you have to change the direction you are going with the piece several times and are still are not satisfied with your work then please just stop for a moment (roughly 90 seconds) and remind yourself that you are good at this and you can do this.
It is more important that you stay sane when writing than it is for writing to get done!
Have someone else read your work.
As much as it might hurt you to do this, it will help because no one knows what is going on in your head so if something is not right or if something is confusing then the outside people will catch it more often than you do as the creator of the piece. I struggle to do this myself, but whenever I do share unfinished works with people they often help me improve more than I ever would have by myself. You are the toughest critic on yourself and you can also be the weakest critic on yourself if you know you were tired or stressed or prioritizing that assignment or piece less than other things on your plate then you will be satisfied with whatever you produce even if it is not your best.
Have a snack or something to drink.
This generally has nothing to do with writing however studies have shown a small correlation between hydration and the length of time you can focus they ave also found some similar findings between hunger and your mental abilities. Hunger and thirst are your body's way of telling you that you need more energy so if you are ever feeling a tickle in your throat or you hear a growl from your stomach then go get a drink or go eat a snack because it will help you focus and stay confident and driven to write at your best level.
Do not write when you are extremely tired, stressed or busy.
As with all things in your life, writing takes time so if it is late at night and you just finished your fifth hour of homework then do not start writing your next thing because you are going to stop in the middle of the piece or sentence and you will be struggling more in the morning to remember what you were saying before you accidentally fell asleep. The human body is meant to have at minimum 5 hours of sleep however the average person requires closer to 8 hours to be at full mental capacity. So if you are extremely tired and you are already spent then just work on the writing later it will always be better after you sleep. Stress is another factor that inhibits your writing abilities because if you are stressed then it comes out in your writing, in most cases. The best writing comes from places of emotion and the best works truly come from your heart so if you are mentally stressed then your writing comes across that same way. It may be short and choppy or just very short in length which is not always a bad thing but it is not the best you can do and you will know that after the fact.
If you are done turn it in.
The hardest thing for real writers to do is to turn in the work even if it is edited 5 times and perfect to everyone else. It is not an insult by any means but sometimes you are just standing in your own way because if you have poured your heart and soul into the assignment then it will reflect even if the writing is not at the same level as Shakespeare, Rowling, King, Green, Carter, Lee, or Faulkner but it is probably far above that which others have done. If you are satisfied with your effort and time spent on the work then it is sufficient for others and that is what is important.