Walking in the Spirit means living a life wherein you daily allow Jesus to be your very "life". Allow your oneness with Him to dominate your every thought and action. Walking in the Spirit is the spiritual quest to be one with Christ through the Holy Ghost. Are you speaking like Him? ...Acting like Him? ...Thinking like Him? Is He becoming your very identity? Not to the point of loosing your own mind... but is the mind of Christ Himself coming through who you are???
To me... that's walking in the Spirit.
1 Corinthians 6:17 (ESV)
17 But he who is joined to the Lord becomes one spirit with him.
All the religious disciplines, practices, and actions on earth do not equate to walking in the Spirit. None of those things that one can do can make certain that one is walking in the Spirit. They are actually fruit of walking in the Spirit. The one who is walking in the Spirit will by nature pray, fast, read, and meditate on God's Word. Seek HIM first. HIM. There's nothing one can DO until they have been apprehended and consumed by HIM.