1 teenager (hopefully not more than one at a time)
1 parent, possibly two because there is safety in numbers
comfy chair, couch or bed
2 ears opened wide for listening
1 mouth closed tightly except for appropriate comments here and there
2 arms for giving hugs
Step1
Find a time of day that is stress-free for everyone to just chat. Don't make this a big issue, unless it is, but if you just feel there is something eating at your teen or you see a problem you want to discuss let them know you'd like to just chat and see how they are doing.
Step2
Next find a place that is comfortable, maybe even your teen's own room, unless you can't see the floor and your safety is compromised. But if at all possible scoop away an area where you can either sit on their floor or on the bed.
Step3
Now comes the tricky part, talking with your teen. Actually it isn't talking that's hard for most parents, it's being quiet and listening. Start by asking your teen about something they are intereted in, projects they are working on, books they are reading, their friends, etc. And really listen and hear what they say. Be non-judgemental, understanding, and compassionate. Remember, try hard I know you can, what it was like as a teen.
Step4
After they have hopefully shared with you, rephrase and repeat what they have said so that they understand that you are listening and not there to judge them. Don't talk too much or give too much advice unless asked for. You could ask them, "Would you like my advice or would you rather I just listen"?
Step5
When the talk is over, give hugs if they are open to receiving one from you. Let them know you are always there to listen to them if they just need to share or vent about something. Carefully make you're way back out of the room, close the door, and congratulate yourself on taking the steps to talk with your teen.