Unless it is carefully worded, advice can offend. What's hurtful, what's helpful...
Hurtful: "You should." If you tell your sister that she "should get out of that marriage," she may get angry if this isn't what she wants to hear... or feel pressured if she's not ready to follow through. Helpful: Ask questions that encourage her to clarify facts and feelings, such as, "If you left, where would you go?" and "How would the kids react?" This helps her make her own choice -- at which point she'll appreciate your suggestions for implementing that decision.
Hurtful: "I had that problem." If you interrupt a friend's story ("I felt a lump in my breast once, too..."), she feels alone because you're not focusing on her. Helpful: Ask for details and offer practical assistance -- "When is your biopsy? May I drive you?" Only after discussing her situation completely should you share your experience and counsel.
Hurtful: "You'll get over it." To move past a problem, a person must face up to it, not avoid it. If a friend loses her job, and your automatic response is, "Stop fretting... you will find something better," ask yourself why. Are you too worried about your own job security to think about her situation? Helpful: Allow your friend to fully voice her hurt -- afterward you'll both feel more ready to explore opportunities that lie ahead.