In my desire to be like Jesus I have to guard against the temptation to merely focus on the external. Addressing the outside of our lives is easy and has nothing to do with real sanctification. Superficial godliness is no godliness at all. It is nothing but a thin gloss over a man's life. A kind of religious manliness that neither addresses or changes the heart. But the other danger is doing nothing, and simply hoping that God makes us grow without any cultivation. Our growth in godliness is a grace from God, derived from our union with Jesus, and is a work of the Holy Spirit, and yet we are active throughout in both killing sin and living unto righteousness. So all the effort, action, and work on our part in the process of sanctification must spring from faith in Jesus and be aimed at our hearts, not just our behavior.
This means we need to grow in faith and communion with Christ while seeking to obey him. One of my favorite books on godliness is Thomas Watson's, The Godly Man's Picture. This work focuses on what godliness looks like experientially and how one pursues it practically. Towards the end of the book he has 8 "rules" or helps for growing in godliness. They are summarized below.
1. Use the Means of Grace.
Be intentional and consistent in the use of the means of grace. Seek to know and become more like Jesus through prayer, Scripture, corporate worship, etc. Use every means God has given you to know him and grow in his likeness.
2. Beware the World.
"The world eats the heart out of godliness, as the ivy eats the heart out of the oak." The world, as a system and kingdom, is at war with the Kingdom of God and the life of faith. Know its dangers and guard yourself against its charms and temptations.
3. Set Your Mind on Things Above.
"Accustom yourself to holy thoughts." Growing in godliness is connected to where your mind and heart dwell. Be sure to give yourself to the biblical discipline of divine meditation on the truths revealed in Scripture.
4. Watch your Hearts.
Guard your thoughts and affections by praying against sin and watching against temptation. "The heart has a thousand doors to run out from," so we must watch it carefully and lead ourselves, again and again, back to the gospel where we find our identity, hope, confidence, strength, and salvation.
5. Guard Your Time.
"Time misspent is not time lived but time lost." It's not that time itself is precious, but that we "work out our salvation" in it, making it a precious commodity. Use your time thoughtfully for all good things: work, recreation, rest, spiritual disciplines, etc.
6. Consider the Shortness of Your Life.
"There is but a span between the cradle and the grave," and this should move us to make the most of our days. God has not promised us tomorrow, but as he has given us today. This realization should promote the priority of godliness as we live now, preparing for the life to come.
7. Make this Your Maxim: Godliness is your Purpose.
"God never sent a man into the world only to eat, drink and put on fine clothes, but that they might serve him in holiness and righteousness (Luke 1:74, 75)." Just yesterday I quoted Sinclair Ferguson who said, "If the glory of God is the ultimate goal of all things, including our sanctification, conformity to Christ is the immediate goal of that sanctification. We are called to be like him. Our corresponding responsibility is to become like him." I like saying we are his to know him and make him known. The pursuit and experience of godliness lies at the heart of that.
8. Surround Yourself with Godly People.
"Be often among the godly. They are the salt of the earth, and they will season you." You need their counsel, prayers, love, and fellowship to grow and remain healthy in godliness. The fellowship of the saints will sharpen and strengthen you.
I highly recommend Watson's The Godly Man's Picture. Get it now to read the whole thing. I also recommend that you hit up the 2012 National Desiring God Conference as they tackle the issue of sanctification. I can't make it this year, but praise God we can get the audio for free shortly after the talks!