"If we say that we have not sinned, we make Him [God] a liar, and His word is not in us."
Sin is an insidious thing. If we acknowledge it, we must confess it and repent of it. If we do not acknowledge it, we sin even worse (by pretending it does not exist). The best thing to do, in confessing sin, is to be as honest with God as we possibly can be. This requires God's assistance.
Confession of sin usually has these two temptations attached to it: 1) to say things to God that we do not really mean (just to ease our conscience); or, 2) to confess things to God which (in themselves) are really not sin at all. Again: the key is candor. May the Lord help us know our hearts well enough, in order to make good confession to Him.
[Puritan quote of the day: "The eyes of our souls cannot be towards Him [God] unless He has cast a gracious look upon us first." --Richard Sibbes, in "The Bruised Reed"]