How to get the most out of writing groups

Just to be sure we're all on the same page (see what I did there?) here's a bit of clarification: When I say "writing groups", I mean "a group of writers meeting to exchange feedback on each other's work".

So there you are at your writing group. It's you and a bunch of other equally scruffy writers. (Okay, just kidding, not all writers are scruffy!) Each person in turn shares stuff with the group and receives feedback.

In my humble-and-probably-wrong-opinion, here are the tips! There are more tips for "feeding back" because it's a skill I think most writers are actually pretty crap at! We spend all our time locked in a room staring at a keyboard, and so our social skills are not necessarily very well developed :-)

As the writer:

1. Bring printouts! At least one copy per person in the group - and a few extra just in case! You're there because you want people to critique your stuff, so make sure your text is put in front of them. Personally I have a dreadful memory so if you read me something I will have NO IDEA what you said fifteen seconds later.
2. Give everyone a bit of context. For example, if the piece is for a competition that's asked for comical stories about treacle, then say so. Otherwise you'll lose 15 minutes of your time to people saying, "So why's it about treacle?" ... and you'll realise that they now have to re-read your work, because they didn't spot anything in it apart from wondering why it's about treacle. 
3. As a side note to #2: It's always useful to stick a line (just one line - don't go mad!) at the top of your work, explaining what you want from the critique... otherwise you'll get told about typos when you really want to talk about plot structure, and vice versa. You might think you can explain before people start reading, but in reality the second you put a piece of paper in front of another human being, they will start reading and stop listening.
4. Have the work read aloud. You can read it yourself, or you can ask someone else to. Hearing it will help you spot problems with the rhythm, with the phrasing - with everything! You'll spot things you'd never have noticed in a decade of silent re-reading. Listen out for where people stumble over your words, or where you've used the same word ten times in the same sentence, or where they automatically correct/adjust what you've written etc.

As the person feeding back: 

1. Listen to what the writer wants as feedback. For example, if they're asking about plot then they probably want you to help them with structural editing, and therefore are highly unlikely to care about typos. Or - if they say the piece is being sent off next week for a competition - then they probably don't want you to say things like, "you should try rewriting this from the washerwoman's point of view".
2. Remember that scribbles are useful! You may prefer to speak your crit aloud, but it's hard for the person to note all your comments in the allotted time. You've been given a printout and you are holding a pen. Make some notes!
3. Shush! :-) Seriously, please make sure you're not the guy who talks too much. There's one in every group - and the more they talk, the less the "quiet ones" talk... which is a horrible shame because the quiet ones are usually the more intelligent people in the group! There's one group I go to where I always end up having to beg the quiet person to talk - because they're too damn shy to speak until the noisy ones hush.
4. It's okay to say you don't like a piece, but please try to give a reason. If you don't have a reason then it's not worth saying, "I don't like this," because it provides no useful feedback to the writer. Let other people talk.
5. Be aware of how sensitive the writer is about their work. Everyone has different levels of writing confidence, regardless of ability or level of success. You might be proud of yourself for being able to receive harsh feedback, but others have not reached that stage yet. There's never a good reason to attack something. Looking back, I'm embarrassed at how much negative feedback I used to give. It's much more fun to find the positive stuff!
6. Say something positive first. This is probably the most important point of all. There is something good to say about ALL writing. If you can't spot anything then it's your reading skills at fault, not the writing. Personally, I'm still learning this, but I know someone with the most amazing talent to immediately spot the positive. And I've seen that every time they do so, the writer in question becomes more confident, and gets better at writing.
7. As a side not to #6: End with something positive as well, if you can. People take crit much better if you sandwich it in the positive. So say 3 things: (i) something that you like, (ii) something you don't like, (iii) something else that you like.