Vary your themes for interest. Vary the way you share those themes - novels, short stories, radio scripts… Vary your style too. You need a mixture of long and short sentences and paragraphs, which can be used to help pace too. Vary what you read - fiction, non-fiction, in your genre and outside it. Not only is it more interesting for your reading life, you’ll be influenced by good writing from a variety of sources, which is bound to help your work. Oh and be influenced by the best!
Communications and Technology
In a fantasy/sci-fi world, how do your characters communicate? I’ve got the Kingdom “borrowing” ideas from earth and adapting them for their use. Could everyday items we take for granted be misused on another world or even be a threat? Could these items be turned and used against us? How can modern communications help your story along?
Brainstorming
Have brainstorming sessions every now and again. If you get stuck with a piece of writing, this is a good way to get going again and who knows what you may come up with? Ask yourself questions all the time. What do you want to write? What have you got to say that nobody else can say?
Persistence
Keep at it. And if you write novels, have a go at short stories on the side. I believe it harder to write a good short story given you haven’t the space to expand yourself that you have with a novel but it’s a good challenge and will help you write tightly, which would do your book the world of good too. Keep your mind and body active and well. Challenges do wonders for the brain. Don’t be afraid to start small and then build up if a novel seems too much to begin with.
Action
Give enough description to make your story real but not enough to drag it down. Does your tale have enough action in it? The appropriate action for what the tale is about?