James 3 says whoever can handle his tongue is truly wise and righteous. I'd like to steal that phrase and say, "Whoever can really handle the law and the Gospel rightly has made huge strides towards joy, faithfulness, and fruitfulness." Not as catchy or inspired, but just as true!
I've found particular help from John Colquhoun and Walter Marshall. Colquhoun's treatment is here and Walter Marshall's The Gospel Mystery of Sanctification is available in the public domain (ye olde version) at www.ccel.org and the updated version from Bruce McRae is available from www.monergismbooks.com.