Every single one of us begin to sin in our minds first. Our minds can be a most dangerous place for us. Don't fool yourself. Capture your thoughts for Him and seek His wisdom.
Check out the whole entry at Eternity Matters, October 19, 2011.
Sins of the Mind
..."the most dangerous sins...there is nothing to keep you accountable to them except your conscience...visible sins are always preceded by sins of the mind"
Matthew 21-22 "You have heard that it was said to those of old, 'You shall not murder; and whoever murders will be liable to judgement.' But I say to you that everyone who is angry with his brother will be liable to judgement; whoever insults his brother will be liable to the council; and whoever says, 'You fool!' will be liable to the hell of fire."...
Advice in digested form:
Feed on God's word
Cultivate the love of God