An unwasted life is one in which you do what God has called or ordained you to do. You successfully accomplish your purpose/mission and you've lived to the glory of God. You also spend your time on things that are eternal, such as human souls.
A wasted life is one where you waste your time on trivial things and do little or nothing of eternal value. It is life spent avoiding God's will for your life.
How can we discern whether or not we are wasting our lives?
By looking to the Bible to see what things the Lord requires of us and whether we are striving for and attaining those things.