Think about the last really good book you enjoyed. If you're an avid reader you might have found yourself deeply absorbed, experiencing the story through the protagonist's senses, picturing the action in your mind, and almost hearing the dialogue as if the characters were in the room with you.
If you read for lengthy periods at a time, you might have felt a bit disorientated when you came to a stop and returned to the real world. This is the ultimate experience of a book and is the effect you want to try to create as an author for your own readers.
Don't jar your reader
While some people battle to read fluidly like this and have to read word by word, your avid reader is able to absorb each concept your words present as a whole. The most important thing to work on is making your writing as smooth as possible. Choppy sentences and sentences that try to cram three different concepts into one mouthful will bring your reader out of the trance.
Words that aren't words
Anything that makes the reader focus on one particular word in a paragraph can interrupt the smooth flow of reading. It has become bizarrely popular among new writers to create character names that are unpronounceable. Worse is the use of apostrophes in the middle of a name. Why would every alien culture choose to present their names in this style? Make yours different. And while you're at it, think of your reader first before you pick names for your characters.
Numbers that aren't words
Another less obvious issue that creeps in is the use of numbers and symbols in fiction. This has followed journalists-turned-authors because using numbers in non-fiction text is actually a very effective technique, especially on the web.
Fiction is a different medium. Try to pronounce "$20" - you’ll find you can't without using letters - ie, "twenty dollars". When your reader sees $20, her brain has to translate the symbols into the words. This draws her attention momentarily - which is the reason it is a good non-fiction technique: it is meant to draw the reader's attention. Don't do it in fiction. And never use numbers or symbols in dialogue. Your characters can't pronounce "$" any more than you can.
For more help with creating the best reading experience for your reader, try How to Grow a Novel : The Most Common Mistakes Writers Make and How to Overcome Them by Sol Stein,
or Make Your Words Work : Proven Techniques for Effective Writing by Gary Provost

