When you are describing a character it is important to remember that you're not just describing what they look like, you are giving a piece of their history. The clothes a character wears is more important than just fabric used to cover their body. It can be used to indicate their social status. The color of their shirt can tell you what groups they belong to. Little details like that serve two purposes: (1) they flush out the character and aids you in world building and (2) it can give you an opportunity to go into their history and backstory.
Ex: In 'Penric's Demon' the author first describes the main character by talking about his outfit. He notes that his clothes are all hand-me-downs and that the character had to hem it himself as well as make his own repairs. This became a jumping off point to describe how the character is the seventh child and third born son of noble house that had fallen on hard times.
This same advice can be applied to describing a place. Every bit of detail that can be added to a town, building, ship, castle, home, or whatever can be used to describe their history, significance, and connection to the characters.
In the case of writing a description of a place where a scene is about to happen, spend a little time beforehand to give a layout of the space.
Where is the door?
Where does the light come from?
What kind of furniture is there and where is it placed?
Where is everyone standing?
All this prepares the reader for what is going to happen in the scene. It primes them with all the knowledge they need so that when the scene happens, there isn't some element that just pops out of nowhere. Therefore when you write this all down be sure to only include the essential details, things that are going to be used during this scene or some follow up one. Don't describe a chair if no one is going to sit in it or use it to club someone.
Tl;dr: Describing a character or place should be an opportunity to give the reader their history and what makes them significant. When writing a scene, take the time to block out all the important elements first.
My esoteric advice: Watch videos of people who make cosplay costumes and listen to them describe every detail of the outfit they're making and how it fits into the story of the character.
write the things you like to write!! the more you love an idea, the more your writing will flow!!
when you read other things, make a mental list of things you liked about it (characters, specific sentences, plot points, etc.) and things you disliked. and then think about how you would write the same thing better!
solid descriptions are really important, but describing every single thing from clothes to buildings to hair to flowers in excruciating detail can really bog down your writing. figure out what things are the most important in a scene and describe those the most!
figure out how your story is gonna be structured! a lot of people do 3 act, which goes in this order: introductions ->the thing that makes all the action start -> a big reveal -> something keeping your characters from the ending -> a big twist! -> another obstacle -> a SUPER BIG DISASTER -> all your characters are freaking out -> another big reveal -> the ending! this is my personal favorite way to structure a story, but you dont have to do it like this and you can switch things around and do whatever you want!! but a story is always stronger when you have some kinda structure, even if its just like. intro -> bad thing -> good thing -> plot twist -> ending.
your main characters should be different kinds of people by the ending of your story!! the things that happen in your story will effect your characters and make them act differently over time. a really happy character might save the day, but lose their best friend at the end - so even though they won, they aren't the happy character they were before because of their loss.
don't compare your writing to other writing! there will always be at least one person in the world that will really like your writing and the only way that person can find your writing is if you finish it and post it or publish it!!
On thing my English teacher told me once was 'Show,don't tell'. Basically, instead of saying "John was angry" you should say "John couldn't take it anymore.His face turned bright red,and his fingers curled into fists. Suddenly,he erupted like a volcano"
I'm not sure if this will help you or not, but I wish you luck with writing a good story!