How to get started as a newbie?

I've been reading fanfiction for as long as I can remember, but always wanted to try writing it. Thing is, as the title suggests, I'm completely new to this and I don't know where to begin.

I'm interested in dabiling on:

-OCs

-AUs

-poetry

-canon compliance

-canon characters being in-character

-interesting (romantic) dynamics (I feel this would be the most difficult)

-sexually explicit content

-so much more that isn't coming into mind at the moment

I just don't know where to start, how to plan it, and generally write out a start/middle/end when it comes to it if that all makes sense?

edit: this goes for writing dialogue and know when to do paragraph breaks too because I'm not sure how to get around that too