Research aspects of the scientific world that interest you, and select a premise that creates an interesting dynamic for your story. Though you do not need to hold a degree in a particular field concerning the topic you choose, you should have more than a basic understanding of the ideas you base your novel on. For instance, if you decide to write a novel concerning outer space, or black holes in particular, you need to research as much as you can about the topic so that you feel confident in the details you present to your audience.
Create a challenge for the characters in your novel. For instance, if your characters are astronauts, travelling through outer space, they need to face an obstacle that allows for both character growth and suspense for your story. Whether it's a struggle like that presented in Orwell's "1984," where the characters go up against a massive, apocalyptic dictatorship, or a challenge like that in "Star Trek," where members of the Star Fleet have to defend the Federation against intergalactic enemies, you need to have a struggle to keep your readers interested.
Come up with characters that make the main challenge more interesting. For instance, if your main character is an alcoholic who also has the tendency to set fires to objects, he'd be a lot more interesting to read about than a character that has no faults. Your audience will relate more to such characters than to a typical, one-dimensional heroe. You also want to create characters that help the protagonist in her struggle against the main challenge, as well as characters that make the struggle harder for her. The more nuanced your characters, the more interesting your story will be.
Develop a basic plot based on the premise, challenge and characters you've created this far. You want to keep the readers interested in the novel by providing suspense and character development, so plot points that enhance these aspects of the book need to be included in your novel.
Write the novel, and enjoy yourself. You can write the novel by creating an outline of the plot points before you delve in, or you can simply start writing with the general information in your head. Either way, try to enjoy the process of developing interesting characters struggling with challenges concerning strange lands or strange phenomena.