"Have nothing to do with the fruitless deeds of darkness, but rather expose them. For it is shameful even to mention what the disobedient do in secret." NIV translation
Since we are children of God who is light, we do not have any business messing around in the dark. As light, we naturally expose things that are hidden in the dark.
"But everything exposed by the light becomes visible, for it is light that makes everything visible. This is why it is said: 'Wake up, O sleeper, rise from the dead, and Christ will shine on you.'" NIV translation
When light appears darkness recedes as they cannot reside in the same place. Light comes from God who in fact is light. God knows all things and, on judgment day, all things will be made visible.
"Be very careful, then, how you live - not as unwise but as wise, making the most of every opportunity, because the days are evil." NIV translation
Paul reminds the Ephesians that they (and we) are to live disciplined lives. We are to be careful not because we are afraid of losing our salvation but because we do not want to miss opportunities. A wise man focuses on things of God which are eternal while the unwise are focused on the things of this world. Each and every day God brings people and things into our lives and we have the chance to demonstrate His love to this evil world. If we do not slow down and look for them (be careful) we will miss many if not all of them and so also miss out on many of His blessings.
"Therefore do not be foolish, but understand what the Lord's will is." NIV translation
We all want to know the will of God for our lives and many pray for it to be revealed to them. It is always good to pray but to really understand the will of God requires more as His will is contained in His Word. There are many that will say that they are following God's will by doing certain things but when those things are not consistent with the Word then they are not in the will of God.