This is without a doubt the most important rule of writing fanfiction:

Have Fun.

This rule has nothing to do with the fact that it will show in your stories if you like writing them, and they will become way better for it. More importantly: Writing fanfiction is a hobby. It simply has to be fun. If not, you are doing it wrong. No matter how many views/subs/comments/upvotes you are getting, you are doing it wrong.

Here, 'fun' can mean every positive emotion, of course, so even if you are not having 'fun', strictly speaking, it also applies if fanfiction is helping you deal with stress or any issue, or if it gives you a sense of accomplishment, or if it simply helps you get mind off things and relax. 

This rule is so important that it trumps all other rules or tips in this tip-shop and everywhere else. If not proofreading your story gives you more happiness than actually proofreading, then do it that way. If making every single sentence in 14 different colors makes the writing way more fun for you, and you want to have every other letter bold and every third letter italic, girl/boy go nuts with it! Your story will be *horrible* to read, but who cares. If you are having fun writing fanfiction, you're doing it right.

There is of course nothing wrong with being occasionally frustrated with your writing or your stories (and getting through those periods can be very satisfying). But overall, writing fanfiction has to give you more positive emotions than negative. If it causing you anxiety, stress or bad emotions, you need to do things differently, or very possibly quit. Doesn't matter how many "update soon" comments or readers you have, this has to be fun for you, otherwise, what's the point?