I can't imagine being the devil, of course! The devil is absolutely opposed to God and His will, which is one reason why we shouldn't become fascinated with him or imagine that he is cute or harmless. He isn't!
But if I were the devil, I would just keep on doing what the devil already does: oppose God in every way possible. God is for good; Satan is for evil. God wants what is best for us; Satan wants what is worst for us. Don't be misled: If a person serves Satan (whether they realize they are doing so or not), they are going away from God and straight toward what the Bible calls Hell. Why would anyone want to serve him?
How does the devil work? First, by deception–trying to convince us that his way is better than God's way. But the Bible warns, "Woe to those who call evil good and good evil, who put darkness for light and light for darkness" (Isaiah 5:20). The devil twists the truth, trying to make us believe that God (and not he) is a liar.
The devil also works by bringing death and destruction in his wake. Jesus said, "He was a murderer from the beginning" (John 8:44). But listen: Satan is a defeated foe! By His death and resurrection Jesus Christ defeated the powers of death and hell. Is your hope in Christ?