I found myself transported back to my history classes at school while contemplating things to write today. “Now, what would you like to do your project on? You can choose anything. What do you want to do? … No, dear, I don’t think that’s appropriate. No, you can’t do that. It’s best if you just do the Spanish Armada like everybody else, I think.” Of course, everybody grumbles when they’re forced to do a specific topic, but better that than be unable to come up with one.
The absolutely fundamental, most important, necessary, vital piece of advice is that you must choose something that you like or that genuinely interests you, otherwise you’re going to have a hell of a time (negative hell) and you’ll give up (unless you’re as obstinate as the worst of mules or, like me, refuse to tolerate self-failure.) Incidentally, this is the advice I was given when I was starting my EPQ. I watched people who didn’t listen to this advice giving up after months’ worth of research or, worse still, halfway through completing the report on the project.
More than this, if you aren’t interested in what you write, it’ll show. Then your reader will get bored because the writer is lacking an interest in the subject.
So. Step number one to choosing a topic: unless you are a masochist, make sure it’s something that interests you and that you like.
Step number two: be honest and reasonable with yourself. There’s that saying “write what you know”. That’s true to an extent, but you can’t really “know” exactly what it was like in the Victorian era because you weren’t actually there. Write what you know and what you can research.
Whatever you choose to write about is going to require research, or at least planning of some kind, even amongst the worst of pantsers. Even if you pants as much as me. My plot plans range between two sentences and two paragraphs (the latter for series). Occasionally I’ll plan by writing out a pitch. Whether you’re like me or somebody who has to plan out everything in meticulous detail (recommended for series), you and you alone know how you react to the idea of researching. For research, if you’re dong historical fiction, you need to be prepared to put in the work, otherwise the story’s just not going to bear credibility, and woe betide you if a graduate of that area of history ever picks up the book. If you know you’re not going to be bothered with the research, it’s quite often worth transferring your idea to a fantasy or sci-fi realm (although even these are not free of research) where you’ll be able to fabricate more – BUT the research still needs to be there. Swords, for example, were not that heavy. Unless somebody is an elf, they are not going to be able to pick up a bow for the first time one day and be a deadly shot felling fully-armoured enemies from fifty paces the day after. Even in the realms of fantasy, some semblances of realism are needed, or the audience becomes too alienated. If something defies realism, it needs an explanation, such as magic or deities or non-humanism.
For people who are planners, they will often find that there are few plot holes to fill in the edits, since they have made themselves think things through beforehand. I’m not saying that plotters are better than pantsers or vice versa, but I do not recommend being a pantser unless you love doing rewrites or are a master of the art of back-writing. You know how you function. If you’re a plotter, choose a topic that will give you plenty to plot about. Intrigue. Deceit. Unexpected twists. If you’re a pantser, choose a topic that leaves the plot fairly open-ended so you can tie the knot at the end of the story after plaiting the strings whichever way you want. If you are a pantser, it is probably not the best of ideas to attempt a detective novel, for example.
Step three: choose something that suits your style.
This one probably doesn’t cause many problems, because your style is most likely going to match what you like best, which will hopefully be the topic you choose. What I mean by this, though, is don’t set something like a general fic or a contemporary fantasy to archaic phrasings such as “desist thou”. Make sure that the tone is fitting to the genre you’re trying to write in. You probably won’t want a morbid first person MC if you’re trying to write a comedy book, for example. Most people try to avoid being too colloquial when writing high fantasies, as well. Stuff like that.
So, to sum up:
First step: Something you like or that interests you (preferably both).
Second step: Something that is realistically within your capabilities.
Third step: Something that suits your style.