Having no sisters, no real life friends, and only one mother, I have very little experience with giving fashion advice. I primarily go shopping alone, talking to myself like a crazy person the whole time. But of course I have gone shopping with my mom before, and any time she asks how something looks I try to give an honest answer without criticism. Fortunately, she is way more critical than I could ever be, so I don't have to steer her away from items with unflattering fit very often. I usually spend more time trying to get her to see when something really is flattering, but maybe a little tighter or form fitted than her comfort zone - I am not usually successful.
Basically my approach is to give any advice if asked, but never offer it unsolicited. Except here on my blog - whenever I have any kind of tip I might think other people could find useful I share it on my blog - that way people can accept it or not and I won't ever really know.
As for taking advice, i rely on the blogosphere and fashion magazines for that. I try to find people whose style I admire and *cough cough* copy what they are doing. Pinterest is a great tool for this as well - I pin pictures of outfits I love and then try to recreate them in my own wardrobe. And if I see someone out and about in something i think is great, I will ask where they got it or what brand it is. Some people are weird about answering, but most women are happy to help - we all love a good compliment!
I think the most important thing to remember about fashion advice is that no one has to take it - feel free to turn down any advice given to you if it just doesn't suit your style, and don't get offended if a person you are trying to help stylistically chooses to ignore you.
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