Do you ever feel that no matter what you say to your teenager, it's the wrong thing?

I have a 17 year old son and a 15 year old daughter. Following their advice, I am trying not to lecture when they just want to talk. I am trying to avoid offering advice all the time, when they just want to vent. I am trying to word things so that I can be supportive, positive, and firm without being offensive, hurting any feelings, or give the impression I'm angry when I'm not. Even when they need a -chewing-out, I try very hard to word things constructively to avoide getting them on the defensive and to try and solve a specific problem rather than to harp on them for no reason. They don't want me to gush over their accomplishments yet feel as if I don't notice their accomplishments if I say nothing. I don't want to go on and on here. But if anyone knows any kind of communication suggestions for dealing with teenagers, I am all ears. My kids are quite intelligent and sensitive (more than they pretend to be) and I am so looking for ways to communicate with them that leave us able to (1) solve the current problem or crisis (or at least come up with possible things to try); (2) help them feel more confident and positive; and (3) know that regardless of mistakes (mine or theirs) that I love them unconditionally. Any books out there, websites, any kind of suggestions. I just don't know what I'm doing wrong when a discussion or talk or even a good time suddenly disintegrates into tears and anger and I'm sitting there stunned trying to figure out exactly what just happened.