When you write, one of the key things that you need to do is to write for your audience and not for yourself.

That is, bear your readers in mind. Who will they be, what background will they have, and so forth.

Clearly if writing for children your style and language will be radically different than if you are writing for adults.

Similarly if you are writing a science book then a certain background knowledge can be expected but if you are writing a popular science book for the mainstream audience then you will need to ensure that any jargon or concepts you introduce are clearly explained up front.

Genre also plays an important part: thus in a fantasy novel people really want to escape the real world and get involved with the creation of your mind, therefore take lots of time to go through details and describe what is going on, something that may not be required in a standard fiction novel.