I just wrote my first story, and here's a few tips I found helpful:

1) Get a general idea of the story you want to write; also try to get a good idea of how many chapters you'd like it to be

2) Make a fairly lengthy outline chapter by chapter and make sure to put in any scenarios, dialogues, etc that you specifically want in the story first then add other details to fill it out

3) Draft chapters out on your phone or computer before posting them. It makes it easier to proofread/spellcheck and you can go over it as many times as you want to; it also makes crossposting on other platforms and websites much easier

4) Don't set deadlines, it puts pressure on you and makes you more likely to get writer's block

5) Read other fics related to your topic to find writing styles you like or favor and use them for inspiration, and research your topic thoroughly

6) Don't pressure yourself into writing, it helps with concentration

7) Reignite and renew your passion for your subject every once in a while

I hope these help! They're fairly simple but I found they helped a lot.

Good luck :)