- Where should I start? Oh, right. DO YOUR RESEARCH. You have even extra material to read. You just read/watched the material, it's fresh in your mind. Great. Research for online debates. I can assure you that a lot only people saw parallels, references, details on the photography or connections between different books or episodes that you can't even dream about. Go read those and get a new and deeper understanding of your fandom. Go read Tumblr, Wikia, check fanarts, read other fanfics. Read the canons, the headcanons, conspiracy theories, find as much material as you can and SAVE IT. Writing a doc, taking a screenshot, saving the url, whatever you want. Check all that info regularly.

- Can you use clichés? Of course. Just try to still make it unique. "I don't know how to make unique". Change fanfic style. You've been reading too much nerd X rebel? Go read Starbucks AU. Or go back to the original. Read the same characters in a different setting. And then think, is there anything in these that I can put in the nerd X rebel? Or maybe think, how can I escape the stereotype cliché while still making sense? Maybe the rebel actually volunteers in a shelter. Why would they? Maybe because they are a rebel they ran away once or twice and realized how things are hard on the streets? Maybe the nerd loves the gym because it's only after they're so tired from the gym that they can fall asleep easily without thinking too much. Maybe they have the same part-time. Maybe they both write poetry. Imagine if the nerd is the one to write nihilist poems, and not the 'gothic' rebel? Use the character's original personality to help guide you to what they would be doing that is not tied to the rebel/nerd/X stereotype.

- You can put all the characters from your fandom in your fic. Or you can put just a couple and fill it with OCs (Original Character). Or a combination of both. Gold tip: give those extras development as well. In my experience, as long as you make round-about OCs, people will like them. And what should you do about these OCs? Write everything down. Go back to Part 2 and reread it. Make also friendly OCs, only evil OCs is tiring.

- What is OOC? Out Of Character. Is when a character in your fic acts different from the original source. A character who is very brave acts like they have too much doubts and not enough courage. Another who is very honest starts acting all fake. One who never wanted to marry is with the wedding date set. It's your fic, you can do whatever you want, but in MY PERSONAL OPINION, this shows immaturity from the author (not immaturity as in childish, but as in not experienced, not mature enough). Why do I think this is immature? (of course, you can skip my rant or read and disagree) Because most of the times when this happens, there isn't an explanation as to why this change of personality (when you could also have used another character from the fandom or maybe created an OC), and there isn't a growth either. If you're going to do it, what I think one should do is present a reason and then giving that character the possibility to grow and become who they were supposed to be. Example I saw being used: a character who is very brave becomes a coward for living in an abusive family (98% of the times this happens, you can see CLEARLY that the author DIDN'T do their RESEARCH, because it's very messed up and not in a realistic way). So... the police don't exist? No neighbors to call them? No teacher or coworker see the blacks and blues and try to intervene? In student's case, no counselor? No Child Protection Service? No friend invites they over and the friend's parent sees it and calls someone? The character really has to stays with that abusive family and then be happy when their romantic interest saves them and everything gets magically resolved in a month after a decade of abusive? Why not giving them a chance to save themselves? To realize that was not okay and calling the police and facing their abuser in court and learning how to be brave? Why the one who never wanted to marry don't have a very sick mother who dreams of seeing their child being settled with a good partner and they create a scam with their friend, the wedding will be fake, it's just for the show? Or maybe they feel pressured by society to get married and at some point, they realize it's not for them and call the whole thing off and go be happy on their own. I think that if you want to make a character OOC, you should have a reason behind it and should give them the chance to grow (the romantic interest maybe give a push or support, but I think friends and family are just as important, even if the growth must be done by themselves, as no one can change you except yourself).

- You should also try to find a rant book. Most fandoms have one or more, where the author criticized those clichés in fanfics that are waaaay too frequent so you know what to avoid from the start (and also may give ideas on how to escape those traps and make your fic unique).

- If you have a more specific answer, you can always comment or PM me (I'm usually very careful to always answer those comments directly to me)