How to Keep From Losing Your Faith

We have probably all known individuals who started out in their walk with God and seemed to really be maturing, but then something happened, and they seemed to 'lose' their faith. Paul refers to the importance of keeping the faith, and not making 'shipwreck' of one's faith. What do we need to do in order to make sure we continue a vibrant, growing faith in Christ? (Note: this is NOT referring to 'losing one's salvation')