Throughout his book On Writing, Stephen King often refers to the "ideal reader". What is the "ideal reader"? you ask. Let me explain.
The ideal reader is the person you are thinking about when you are writing. On my first book, Defensive Tactics, my wife Mica was my ideal reader. As I was writing, I found myself asking, "What will Mica think of that", or I would imagine her laughing at a particular joke or scene. I was writing for her appreciation and to her sensibilities as she was representative of the general audience I was attempting to appeal to.
On my second book, Crater Lake: Quest for the Prison Key, my ideal reader was my 11 year old daughter. Crater Lake was written for a different audience in general, but just like on the first, I found myself wondering, what will Lindsay think about this or that, and I wrote scenes that I knew she would appreciate. What will scare Lindsay? When I figured it out, I wrote it. What will make her laugh and what will she think is dorky. I tried to avoid the dorky.
Even though my ideal reader was different for these two books, the concept is the same. I couldn't wait for them to read what I had written for them and ultimately, when I was finished, I listened to their feedback and made some corrections where I had miscalculated.
Thinking of someone you know well and respect, and what their reactions will be to certain content, can help guide you in the writing process. It places the focus on the reader, instead of the author. What the reader enjoys and finds funny, or frightening, or exciting and cool, is much more important than writing something that only I find interesting.