Have dabbled in it and can confirm, betas are a life saver. Pity mine doesn't talk to me anymore but oh well.
That aside, writing is very much a discipline that takes a long time to learn. Story arcs, character arcs, prose, themes, these are all tools you at least need to know about and utilise to some extent. I've spent a few years looking these details over in my spare time, and whilst I'm still a total neophyte, looking back at my old work makes me cringe given what I know now. I believe a lack of understanding for these tools is more often than not the reason for why fanfics spiral so wildly out of control.
Also, some advice as someone who's sort of been there and done that, plan for fuck's sake. Gardeners are wrong, G.R.R Martin lied to you, you have to know where you are going or else the story devolves into disorder. Just spend a month or so with pen and paper figuring things out and it will demonstrably improve your story.