I have some green and orange items I can't use. Should I just sell them, or should I try to trade them? So far, I have just been selling them, but they might be items that others want.

For example, I have a green power gem. Since I am all dexterity, I don't think it is worth anything to me. So how do I go about finding someone with a dexterity gem to trade with?

Do guilds make trading easy? I have received some invites but haven't joined.