Ever read a book where it teems with life, where you can really feel that things are happening beyond the page, as if you're viewing a window on a world that lives and breathes whether you read about it or not?
More importantly, is your writing like that?
Because it should be, as this is one of the three techniques that trump every other in writing.
So how do we go about achieving that? It's simpler than you might imagine
Don't show the details, know them
Convincing worlds aren't about dumping everything you've researched or made up onto the page. Showing the full extent of your world doesn't make it impressive, it makes it small and knowable. What you reveal about your world in your story should really only be the tip of the iceberg.
This doesn't mean you don't have to do the work – the more you research your supporting material the more you'll achieve that 'world beyond the pages' feel. If you can fit all the material you've created in the book then it's likely you haven't done enough work at best, that you're boring your reader senseless at worst.
Don't just write with words
Take pictures, draw maps, invent languages. It makes a change, develops your world, and you're less likely to use that kind of work directly in the text. If you have a picture of your protagonist's garden, you know the exact layout of his house, the clothes he wears, how he reacts when he burns his toast, then that knowledge will show without you having to detail it.
Best thing of all, if you have that kind of material then you can focus on the story when you write it. More than likely if you've done that level of research, the story will write itself.
Produce a guidebook to your world
Ever played role-playing games? Ever run them? Do you even know what they are?
Writing material for a role-playing game is an interesting challenge - you don't know the main characters or the main narrative - these are created by the players themselves. All you can do is invent and detail the world, populate it with deep and interesting characters, present challenging scenarios and give the players a reason to be there. This forces a distinction between the story-world and the narrative - it encourages the writer to imagine the world dislocated from the story that will happen within it – particularly useful if you're planning a series.
Take a holiday
Sometimes you'll feel drained by developing your characters, exhausted with working out the intricacies of your plot – that's the perfect time to start travelling, discovering, and detailing your story-world.
And the cool thing is, your narrative and characters will be the better for it.