EducationI probably should have put this into the "society and culture" section, but I wanted education to come after you've developed a sense of your speculative element. After all, if you have a character who is intimately connected to that speculation (a wizard, perhaps, or a scientist), then you need to know what kind of knowledge they have before you decide how they would have gained it.
This, fortunately, also ties into character development. If you don't know anything about your characters yet, at least you'll know, when you come to that, what a typical educational experience would be for them.
So, what kind of educational system does your society use? Do apprentices train in a particular trade before graduating to journeyman or master level? Does a child learn the profession of its parents? Do churches or religious institutions educate the children, and if so, do they educate all children, or just the religious or wealthy ones? Are there colleges and universities for advanced studies? Do students learn in a virtual reality world, and if so, do they have the same kinds of conflicts they might encounter anywhere else?
One of my favorite books this month is Sabriel by Garth Nix, because the main character grew up in a turn-of-the-century-technology boarding school where girls learn their letters, etiquette, math, science, but also fighting and, in some cases, magic. I love this book because the author didn't just stick his heroine into an apprenticeship, nor a convent, and didn't have her grow up in the modern day world with all its conveniences, only to be teleported to his story's real setting. Instead, the heroine grows up in a place where she can have a relationship with the story's setting while also being somewhat separate from it. Thus, when she goes home, she is prepared but still unfamiliar. An alien native, so to speak. Her education has made her an outsider in her own homeland. It is a crucial part of her character, and she could not be Sabriel without it.
Ender's Game is another excellent book for making an educational system be an integral part of the story. I'm not a fan of genius child protagonists, but I liked this novel because Ender encounters a new educational system, along with all the pressures of being in a new school and being the new kid and the small kid in his class.
Whether your novel is fantasy, science fiction, or even horror, your characters will probably have had some sort of education. It's a human universal to train our children to do something later in life. Decide now what kind of schooling is available in your world. Decide how your characters have been educated, and in what kinds of subjects. And don't focus so much on their specialty that you forget that they're people.
You may discover that you want your character to have pursued one particular field of study that isn't relevant to his or her life now, but which was an interest to them. That's great-- most people do not focus on one field of study to the exclusion of all others. If they did, you wouldn't have this world-building exercise, and a lot of great advances that rely on two or more fields intersecting would simply never have happened. You can even insert that kind of synergy into your novel (imagine the physicist who has a passing knowledge of art history-- enough to know that his time machine has taken him to a certain date, based on the architecture around him!)