Someone on AO3 asked me for writing tips since they want to start writing fics for the first time. I kinda wound up typing out a big ol' eleven paragraph essay of advice but my sister said I should post here so more people can read my tips. So uhh if you're interested in some of the tips and advice I've got, you can read my reply below the cut!
I will definitely say planning is important. I've noticed that if I don't have a decent outline that'll take me from start to finish it's harder to actually write the whole thing and it often winds up an abandoned project - having it even more fully planned is preferable but I often have a few gaps where I'll have to figure out how to get from plot point C to D or whatever, which can be annoying to figure out down the line, hence I recommend getting it as fleshed out as possible first.
Write what you love, that's another big one. Start small if it's intimidating - just like, a oneshot, a scene that you think would be fun to see between some characters you love or something. You could always look up writing prompts if you need inspiration. And, of course, reading is a huge help! I can't imagine being a writer without having read plenty of things myself - and read with the mindset of writing too. Like, reading for enjoyment is great (though since I've been writing since I was like, 12 I think I technically always read with the writer's brain somewhat active LOL) but taking note of things you like about how others write as you read can be really helpful. Like artists using other art styles as inspiration!
Also keep an eye on things like punctuation, spelling, grammar, etc - I'm certainly not perfect at it, but if you make a lot of big errors it can really distract a reader. I like to use Grammarly to help point out mistakes that I missed, but a word of warning, it's not always accurate, so definitely don't just accept everything it says as correct. It mostly helps me to see areas that *might* be wrong so I can see whether or not something actually needs changed. One mistake I tend to see newer writers do a lot is failing to make new paragraphs where they should. So be sure to follow the P rule - new Person, Place, Perspective, Plot point, Point of view, or Period of time are all moments when you should be making a new paragraph. So read up on basic grammar/punctuation/capitalization/etc rules and maybe even look up common mistakes people make so you can keep an eye out for it in your own work!
A trick I've found handy to help with writing characters if you're having trouble keeping them in character is to do a character study. Look at what's happened to them, their personality, and write about the whole thing. From their perspective, preferably. Try to get in their head. What makes them tick? What makes them who they are? What events have shaped them?
When it comes to dialogue, I encourage reading the scenes out loud after you write them. Does it sound natural? Does it sound like something they wouldn't actually say? Reading what you've written out loud in general can help you catch mistakes or areas that don't flow right, and if you've got someone you trust to read to, definitely do that - they might point out areas that don't make sense to a third party reader but only made sense to you because you already knew what you meant.
Don't be afraid to use a thesaurus, but don't get crazy with it unless super wordy purple prose with extravagant language is the style you're aiming for LOL use it where it really counts! Not all synonyms have the same feeling and vibe so keep that in mind when deciding what words to use. And do NOT listen to people who say said is dead. If you try to use a descriptive dialogue tag (aka stuff like mumbled, shouted, cried, sighed, etc) for every sentence it's gonna start sounding super weird. Our eyes and brains tend to skip over "said” because it's so basic. So if you need to make it clear who is talking (and you do want to make it clear so people don't get lost in ten lines of back and forth dialogue while forgetting who is saying what) without trying to figure out a special way that person can talk or some action they can do while speaking just so you're not saying "said", don't worry about it. Said is not bad, it's very useful. Save the dialogue tags for when someone is talking in a specific manner that's important to the tone of the story. If they're upset, make it clear in their voice or mannerisms. If they're extra excited or really angry. Use dialogue tags where you actually have something to get across.
I also advise trying to show not tell. Like yeah, some things need to be outright said sometimes, but there's plenty of ways to show things. Don't say "he was mad" if you can say "his fingers curled, anger blooming in his chest". "Thinking of her dead father made her sad" could be "her eyes started to burn with tears at the very thought of her late father's passing". I also recommend avoiding the extensive character physical description all crammed into one or two paragraphs the moment you meet them fjkfkgkgk you can sprinkle in their appearance over time. In one sentence, you can use something like "her blue eyes met his" and then a paragraph later, "shoving her black hair behind her ears with a huff, she (etc)". Unless it's really important to a character, it's not necessary to know what their entire outfit looks like, you know? Unless it helps show who they are or really stands out. It might be good to mention if it makes it clear what they do for work without having to outright say it, or if it helps paint the picture of their personality or life style. But it's not always needed or important. Learning to cut out stuff that's not actually important to forwarding plot or character growth and things can be really challenging (I try and put those in a different document in case I can use them another time or at least draw inspiration from them) but it is good to eventually learn.
What else... Oh, action scenes, if you ever want to write those, know that the more detailed and descriptive you get, the slower the scene will *feel*. This is something that's really fun actually, once you start to get the hang of it. You can have part of the fight feel like it's flying by so fast, wham bam kick just by keeping it within a few sentences. And then you can draw it out a bit more using more descriptive words and actions for another part of the scene. It's neat to play with the timing of things using that method - which can apply to more than just action scenes, but I feel like it tends to be easier to notice during those.
Also, write literally anything down that you come up with and think, oh that's kind of fun! You might find a place for it somewhere eventually. Don't be afraid to write scenes out of order - you can always tweak them to fit later! I've got a separate document for each story I write that's basically just future scenes or lines I'd like to fit somewhere if I can. Don't think there's no point in writing something down just because it's only one sentence. If it's a sentence you like the sound of, it might come in handy later!
Most importantly, practice a lot and don't be afraid to write badly. Like, it's all just steps towards getting better! Everyone starts somewhere! You might suck at first and that's okay - I can't even begin to express how horrible and cringey my writing was when I first started LOL it was like the kind of fanfic materials you see people making fun of and mocking. But I loved writing so I kept doing it and over time I got better! Just like any craft, unfortunately, it takes time and effort and doing it repeatedly (regularity can certainly help - sometimes I feel rusty if I go long periods without writing a single thing). Writing when inspiration strikes is always great, but sometimes you'll find yourself completely without inspiration, and when that happens, sometimes you just gotta force yourself to put pen to paper or fingers to keys and do it anyway. You can always go back and revise and improve later, or rewrite the entire thing if you don't like it, but something is better than nothing. If you hate what you wrote, ask yourself why and look for what it is you want to improve.
I mean heck, I've been writing for, what, over a decade? And I write stuff all the time that I look at and go hhh yeah,,, not the proudest of that, I could do better, I HAVE done better, etc, so even if it's been a long time you'll probably have those feelings plenty, but I think that just comes with creative hobbies because I certainly feel that plenty about my art too LOL don't get too discouraged though. When you read something that makes you go man, I wish I could write like that :/ my stuff sucks in comparison :/ try to think about what it is that's so good about what you read. What it is that you'd love to emulate into your own stuff. Is it the descriptive terminology? Is it the plot? Munch on it and try to figure out how you can use it to improve rather than just get discouraged about your stuff.
That's all I can really think of at the moment as far as the kind of general, all-encompassing sort of advice goes + some extras I just feel like I've picked up over time that I don't see talked about a ton in general writing advice... But if you have any questions, feel free to reach out! I love writing and I love to see people get into the craft <3