A lot of writers have a certain message they would like to put into a story. That is all fine and well, but it is important to remember that the story must come first. No matter how strong or important a message you may have, it will not be heard if the reader doesn’t finish the story.
Plot first; always. Which means that you must have a plot, one in which you do not have to force your message in, but a plot into which the message will slip in naturally, almost not be seen. Your message should accent the plot, never ever overwhelm it. The plot is what the reader is there to read; if he knows going in that it is a “message story” then chances are he can guess what the message is before the first chapter is finished, tell himself that the rest of the story is just a bunch of old preaching, then put the book down.
For instance. When was the last time you had any interest in a movie that screamed “Drugs are bad for you” in the opening credits or the trailer? The people already sold on the premise don’t need to see it and the others will figure it’s a big waste of time. Better is to hook them into a really good plot before they realize what you’re really talking about.
For myself, I have written really long epics where the main point is the plot and entertainment, but at one point or another I realized that one segment or another of the story could draw a parallel with real-world events. At that point I “accented” my story a little in that direction. Nothing to spoil the plot or hit the reader over the head with a hammer, just enough to get the read to think like I had in that “Hey, this reminds me of…”
So, if you have a message to tell and want to bury it in a good piece of fiction, remember plot is always king. Throw in a message here and there if it fits into the plot, but do NOT make the plot fit the message; the reader will see it and recognize it as artificial and forced. If you can’t work in your desired message, then you need a different plot.