I'm not talking about opinions as in, "you look beautiful today" (unless you want to state the opposite) - what I'm talking about more is advice, and that applies to both good and bad advice. Why good advice? Because "good" is subjective. A parent who constantly gives their opinion to their adult child, for example, probably thinks they are doing something good, but it's questionable whether the child thinks the same thing.
It doesn't feel good to get opinion after opinion after opinion about something when you have not asked for it. We have all been on the receiving end of unsolicited opinions, and yet most of us continue to give our own, unsolicited. I don't believe it's from a lack of caring - usually it's the opposite - but we don't know how it will be received in that moment, and so it is often not a loving thing to do, no matter what the situation.
A good rule of thumb, if you're dying to give your advice to someone, is to ask them if they want it. You will be surprised how often people will say "yes" and how often they will say "no." When asked, most people will answer honestly.
Asking if someone wants your opinion accomplishes a few things. First, it makes the other people feel valued (ironic isn't it - you were probably wanting to give your unsolicited "good" advice precisely because you value the person). Second, it helps you feel better about yourself. Third, and probably the most powerful in the long run, it helps you establish clear boundaries around the whole issue of opinions. The end result of having clear boundaries is that when other people give you their unsolicited opinions you realize that those opinions are theirs and you don't need to take them in or be ruffled by them if you don't want to.
It's sometimes hard to remember to keep your opinion to yourself - or ask if someone wants to hear it - but the more you do it, the better you will feel not only about you but also about the people in your life and your relationships with them. But then again, that's just my opinon...