I often rail against narcissism here at Quick Writing Tips. I do it because there's so much self-centered junk out there that it drowns out the writers saying something worthwhile.
But don't let the fear of being narcissistic stop you from writing. Don't let it become another obstacle between you and your goals. If you're reading this blog--and specifically, if you're reading this post--you will never have to worry about narcissism in your writing.
Why? Because this problem only happens to writers who never think about it.
If you are honestly concerned about your writing being narcissistic, then by definition you are not. A true narcissist would never conceive of worrying about his own narcissism.
The fact that the idea crosses your mind is sufficient to protect you.