Storylines and How to Choose Them

                                    

                                          
Let's say this first: if you're simply going to make your character join Harry & Co. in all their adventures, and not change the plot much except to add another character and make it a Golden Quartet...
                          
Your fanfic doesn't really need to be made. 
                          
Trust me, I've imagined those plots all I could. It's really fun, seeing yourself (or your character) with the Golden Trio. However, it's nothing new at all. The point of fanfiction is to take a pre-existing storyline and tweak and change it, to create a new story from it (unless it's a romance fanfic... Or a specific character's story... But you get the idea). If your story doesn't add anything new except a new character, it shouldn't be made. Now, I've gone so in depth on this topic, so I'll leave it at that. 
                          
I'm sure by now you're all wondering, "How do I do that? Create my plot? It sounds hard." Well, it sounds hard because it is hard, or can be. But you just have to sit down, do some thinking, and decide how your character's life will go. 
                          
Every person is the main character of their own story. You know that. They're supporting characters in other people's stories, and love interests in others, and even villains in others. It all depends on this amazing thing called perspective. If you want to make a fanfic about the years Harry was at Hogwarts, the very least you can do is give us an entirely new perspective. Tell the story through Cedric's eyes, keeping in mind that naturally he would have seen himself as the main character. Sure, Harry might be greater than your characters, but that's okay! Have you ever been in a place where there wasn't someone who was better than you? But you didn't simply narrate their story. No, your thoughts centered around yourself, and what was happening to you. For this kind of story, you simply need to think about how all of this would have looked from their eyes (and the difference may be huge) and, if they're more a Cedric rather than a Hermione, come up with other, completely separate things to happen to your character, or for your character to cause. 
                          
Now, say you want to create a Second Gen fanfic (or any fanfic at any time period where Harry wasn't at school). In some ways, this is much easier than a different perspective fanfic. In some ways, it's much harder. 
                          
How is it easier? Well, there are much less restrictions on what you can do without breaking canon (though there's nothing wrong with breaking canon!). You'll never be tempted to simply retell Harry Potter with a new Harry. You have a lot more freedom with your characters and plots. 
                          
How is it harder? You basically have to come up with a plot from scratch. And it better be a good one, too. Novel quality. Why? Because you're telling a story. Any story needs a good, solid plot. I'll have a chapter about the basics of plots later, but for now just know that you need a plot, despite the fact that this is a fanfic. 
                          
So, say you've got your perfect Second Generation characters. Your romances are all planned out, and you're itching to go, but you still haven't found a good plot yet. Anything is possible, less is probable, and only you know what you need for this story. The trouble is, you're out of ideas. This lack of inspiration can often make authors turn to Voldemort, and have him somehow return from the grave. Unfortunately, not only does this not make sense, but it's boring. We don't want Voldemort. We saw enough of him. Harry killed him, and bringing him back simply makes all the deaths in the Battle of Hogwarts pointless, and undercuts the amazingness of that last book. So, don't bring Voldemort back. Make the newest dark wizard rise if you want to. Give him a believable problem with your main character, and you've got your antagonist. Give him a believable reason for whatever he's doing (world domination is a little overdone, but ridding the world of muggles is a sure and simple one). Give him believable strength. If he's only come up now, as your dear little character enters first year, he can't be as powerful as Voldemort was yet. Sure, maybe he's been working underground for years, getting support. Maybe he's still underground and your character only finds out accidentally. But the thing is, if he's been out in the open, being the next Voldemort, before the events of your book, then it's silly to think he'd waste his time with a first year (and no prophecies should be used, because that's highly cliche too!), or that the aurors aren't already leagues ahead of your main character in defeating him. 
                          
Your main character needs to be the central cause of your story. Things can't simply happen to her. Some things need to be her fault. Some things need to be intentional. She has to be given a choice, and sometimes she has to make the wrong one. There need to be consequences. She needs to make things worse before she makes them better. And she (or her parents) should be the reason the antagonist is targeting her as the next Harry Potter if you're writing that kind of story (which is the only way you could go with a Next Voldemort story, honestly, if the Next Voldemort is your central antagonist). 
                          
There are so many other types of plots and stories that I wish I could get into, but unfortunately, that would take forever. I'll leave it here, with the reminder that the most important aspect to your plot is planning it!
                          
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Did I miss anything? Do you have any tips or tricks you use? Let me know in the comments! And let me know any topics you'd like me to cover, or questions you have!