Ethical dilemmas can keep you up at night, worrying about what's the right thing to do. The problem with ethical dilemmas is that there's never an easy answer to this question. You have to weigh your moral code of conduct with the consequences for the people involved. Here's how to solve an ethical dilemma.
Consider your own motives and try to detach them from your decision. If your ethical dilemma is whether to tell your friend's husband that she's cheating, your instinct might be to keep quiet rather than potentially lose your friendship. Take your own feelings out of the equation and focus on consequences to the involved parties.
Consider your moral code of conduct. If you're pondering ethical issues, you must have a strong sense of right and wrong. Ask your conscience what the right thing to do is. See if that makes the dilemma easier to solve.
Think about the consequences--what will happen if you come down on one side of the moral dilemma versus the other. Consider whether anyone will be hurt or will suffer unjustly. Also consider any secondary parties involved, like children. Telling the boss that the janitor did a bad job in the conference room might force an inadequate employee to take responsibility for his actions--but if a family living at poverty level loses a paycheck over one sloppy job, it might be worth it to suffer through a little more dust than you prefer.
Listen to your gut. If your instincts are telling you the right thing to do, by all means follow them. That's what instincts are for.