4th July 2012 Update: This guide has been updated so it is more relevant to the community now.
The shortened URL for this guide is: http://bit.ly/ggcommunityadvice
So hello and welcome to giffgaff! 
Being one of giffgaff's main USPs, I'm pretty sure you can't wait to get going and earn some payback! But someone ought to tell you... there are users who attempt abusing giffgaff's system.
What we don't want is for you to innocently pick up their sly ways and learn the wrong things from them - it's no good for you or anyone else, and it just results in utter chaos and confusion!
So here's some of the most common misunderstandings...
1. Observe the forum first - When people say 'observe the forums for half an hour or so before posting to get a feel for it', your first instinct is to dismiss this advice... Well, actually, it's more useful than you'd think. Don't ignore it, because doing this means you're more likely to post better quality posts, and hence earn more payback!
2. Do not just post 'Ask an agent'. - I cannot stress to you enough how important this is. You often find that many new users take to posting this on every question because they believe 70 billion posts means top payback - This is not the case. Payback is earned on quality, not quantity. The agents will only send the OP (original poster) back to the community. Of course there are sometimes situations where people do need to contact an agent, e.g. when they think they've been charged wrongly or they want to port their number (i.e. account related queries). But don't adopt this habit of posting it to everything - it only means that the people who really need help from the agents have to wait longer.
3. Settings Text Misunderstanding - Another common misunderstanding is 'Text SETTINGS to 2020' - This settings text is only for MMS and internet settings on standard phones; not for iPhone, Blackberry or Android phones, and they don't affect SMS or calls. Not being able to send SMS is more likely to be related to something like signal, credit or uncompleted number port. Again, have a read round the community to wise-up on certain subjects.
4. Don't accept your own post as the solution - If you've asked a question, people will reply and try to help you as much as possible. Now, when they've all replied and assisted you, you may post something like 'Thanks'. You'll then find a button labelled 'Accept as Solution' in the bottom right hand corner... But it's on all the posts other people have made on your question! You can only accept one person's answer as the solution - but don't accept your own post as the solution! Find the post that gave you the most useful information and choose 'Accept as Solution' on there. Now and then newbies choose their own because they don't realise it chooses that particular post, but when other users have gone to the effort to help you, it's better to give them credit for it. It's important to choose a solution, as other users having similar problems to yours can see what the answer is.
5. Kudos - If you think more than one person has helped you, you can click on the star under their name. This is called giving kudos. Kudos doesn't affect payback, but the most valid contributors have the most kudos 
just a thought, it's a nice little feel-good reward for those who have helped you.
6. Manners don't cost - You'll often find that people are more willing to help if you ask them nicely. You'll also find that people appreciate it more if you reply to their queries nicely. One of the great things about giffgaff is that so many people use the network, from age 8 up to age 88. This means that not everyone will know what other members consider as 'the basics' of using a mobile phone. So, even if it seems a daft question to you, don't laugh, and just try to help them understand a bit more. Telling people to 'give up and change networks' isn't going to do anyone any favours, especially yourself - at the end of the day, you're the one who is earning payback, so try to be nice to the people that need it!
7. Do your bit! - Sometimes a user becomes especially aggressive and insulting. Or you see someone who is trying to game the system by posting lots of questions and giving themselves the answer. Or you feel someone is using a lot of copy and pasted answers. You can report this by clicking on 'Options' then 'Report Content' - this will notify the Educatorsand quietly PM the membery feel needs editing, and quietly PM the member to tell them why this was. No drama, no fuss, and a nicer, more efficient forum to find the answers to your problems
These guides may be useful combined with this guide:
Guide to kudos: http://bit.ly/giffgaffkudos (by saeed_atcha)
Guide to payback: http://bit.ly/gg-payback (by chriskm, sarahtis, woodyuk & jack17938)
Guide to earning maximum payback: http://bit.ly/giffgaffmaxpayback (by trudiw)
Guide to community terms and conditions: http://bit.ly/communitytc (by the giffgaff team)
Excellent post and very informative. Hopefully it will serve towards eradicating all that is gaming 
and at the same time reduce the unneccesary burden on the agents -- who get a lot of stick when it clearly isn't all down to them when queries aren't answered as quickly as they could be.
Can see you have put a lot of effort into this and it deserves to be "stickied"
Well done you 
