Well... lets see... I read fanfiction... well, attempt to anyway. The problem with it is usually poor structure, poor grammar, poor characterization, poor mechanics, and poor use of established characters. Been browsing fanfiction for well over a decade now, and, yeah, over 90% of what is written is pure unreadable garbage. Too much fanboy and fangirl crap goes on in the fanfiction scene. I hate self inserts, I hate almost every OC, I can't stand OOC characters, I can't stand AU, and I hate head cannon. This is just me, though. The other problems stem from god awful grammar and spelling... So, I have found a way to limit myself to help filter the garbage easier.
Step 1: Limit yourself to things you want to read.
Almost all fanfiction has to deal with romance in some way. No way around it. I like romance (saaaaaaaap <.<) so I stick to only the pairings I can stand... almost all of them are either canon or close enough to be considered canon. This prevents any crazy rabid fangirl/boy from destroying all my sensibilities.
Step 2: Read the Summary
This is a good place as any to tell if you will like the story. I have quite a few limits for this.
1) If it says AU, SKIP
2) If it says OOC, SKIP
3) If it says OC, SKIP
4) If it has other nonsensical pairings listed, SKIP
5) If it has horrid spelling/grammar where it is barely readable, SKIP
Now if it passes the litmus test, we click on the story and start reading.
1) If characters do not act like they should when put in certain situations (usually because of some really stupid fluff), STOP
2) If grammar stays too consistently bad, STOP (Usually I give it 3 strikes for major offenses)
3) If the story pacing is too sloppily put together, STOP
And following these restrictions will yield you the best possible results. Found a whole lot of very well put together Soul Eater fanfiction doing this. No other series that I check up on has shown as many results as that fandom has for me. Each person is different, though, and really, if you want to read the other crap I can barely stand, then that is your business... just do it if it is at least structured properly... no excuses for reading and giving good reviews to crappy spelling, grammar, and plot problems... so avoid 99.9% of Naruto fanfiction. All the limits you put on it and you will still wind up with garbage.... <.< Though I have found a couple stories that did a better job than the actual author of said series at this point, so... I don't know anymore. XD