Everyone knows to insist, just write what you know. Finally you want to not write about skydiving without realizing it, falling fast means that the bridge not through the nose can breathe. You have way to suck in air through their teeth. This small detail changes the dynamics of the whole scene.
With this knowledge will be a full discussion fall almost impossible, not to mention, the whisper of relaxed wind past you.
Readers who have been parachuting or who has voted, knows not the second that something in history.
It's everything from the time of Church, the emergence of a certain place or to fight. In many books, especially science fiction and fantasy, there are fight scenes. Someone hits someone more raises or brandishing a sword and that despite the fact that many people do not know if something is wrong, that those who call because you are in it and can even stop reading because it.
There is an easy way to stop this.
They do what you want to write first!
Go and try it, or at least talk to someone who has the scene that you write an authentic feeling that obtained otherwise. If your characters with swords for a kind of struggle and learn some techniques, when they pull a shot of the canons of the range to go and see how felt the gun in his hand. Need more than one person, to try things, find a good friend or spouse and they have to help you. The original request can be felt strange, but once it starts it's very funny.
This advice is only available for those things that you can do. If you have a race with space or some strange creature created for his book have not of course, see it through first hand experience. The good news is that nobody knows these things first hand. The key to creating rules for his creatures and their world, and never rest.
When writing fantasy and science fiction, there is some room for manoeuvre for options, things occur, but it is believable, at least has the readers think and you ask, "How is possible?"
Each world has its own physics, your own creatures, its own structure. Think of the Earth. Gravity is a given. It was always there, always. In fact, it is a fundamental physics, float law to do things, not just the planet. In fact, each object has its own field of gravity, other elements of the drawing to. It is a universal law that everyone understands and assumes.
But perhaps in the world of this law is not stone. What happens when a declined form of the things of the world? (This would have explained so that the reader does not confuse is). The switch would change everything and you have to push a logical and credible reason for the world, the people of the Earth.
Make sure that what you write, not easily guessed or there to pick up the people, even if these people its critical partner or an editor not (even at times things Miss professional editors).