This is a great (and short!) article by Dr. Richard Pratt on the regulative principle. The RP says basically that the only worship that is acceptable to God is that worship instituted by himself as prescribed in his word. I know this sounds like a "no duh" issue, but the truth is, there are hundreds of years worth of arguing over such a claim, and how to actually apply the principle in worship.
I encourage you to enlighten yourself by reading Dr. Pratt's article.
-w