Imagine you have found a bug in your Debian running KDE, a nasty one, and you want to get it resolved. What you should do?
This is centered on KDE and Debian but most of it is useful in general.
First Case: You have a problem and you have no idea whether it is a bug or not. Even worse, you don’t know which package to report it to.
This happens more often than you might believe; it even happens to experienced people. Your first step should be to checking user forums and mailing lists  to see if someone else has encountered the same issue. You might find that your problem is already known (and maybe easy to solve).
In the case that you do not find your problem there, then you can ask for help and post a mail or message explaining your problem. Pick one mailing list or forum board, the one you think is more appropriate, then post your issue there. The most detailed you are about your problem, the bigger is the likelihood of you obtaining help.
It could happen that:
- you are told how to solve your problem. yay \o/
- your problem is not a real bug in Debian/KDE and you learn why.
- your problem is not solved, but you are at least pointed to the software that is causing it.
- you do not get any answer.
If you do not get any answer it might be that nobody got into the same problem and they do not how to help you. But it is also possible you were not clear about your problem. Also, you need to be patient; it is unlikely someone will answer your question 2 minutes after you posted it.
If you find out more about your problem, it is a good idea to send another email or post updating your first message. If after 5-7 days you do not get any answer, you can try asking for help in another forum or mailing list.
If you are given pointers to what software is causing the problem you can go to the second case.
Second case: You know where the problem is. Where you should report your bug?
First, you should check in both the Debian and the KDE bug tracking systems  to see if the bug is already reported. If that is the case, and you are able to give more information about it, update the bug report.
If the bug is not reported, then report it in the KDE bug tracking system if you think it is a problem in the application or in the Debian BTS if it is a packaging problem. If you’re not sure what kind of bug it is, you can go to the first case (in the beginning of this post) and ask in the users forums and mailing lists .
However, you won’t always get it right, and in some cases you will be pointed to the other bug tracking system. Do not take it personally; KDE developers can not help you with packaging problems and Debian packagers can’t always help you with the application bugs.
It might be that your problem is solved in the development version, so if possible check what is going on in the development version before report.
When reporting the problem, give all the details you can about your problem. If you can detail the steps to reproduce the bug, even better. Also, if you are asked for more information, reply the best you can. Somebody is trying to help you. Be nice !:)
Also, remember to be patient when reporting bugs or being asked for more information: both KDE and Debian are big projects with a lot of traffic on their respective bug reporting systems (esp. KDE), so sometimes there is not a quick reply from the developers.
In Debian, a lot of people report upstream issues in the bug tracking system and they think it is good and what they have to do. The truth is that in a very few cases, such as security bugs or data loss bugs, this is a good idea. But most of the time it is not useful to report problems to the people who can not solve them. Do not expect Debian/KDE maintainers to forward your problem upstream (a problem which they may well not be able to reproduce), then back to you when upstream ask for more information, then back with the information to upstream… it is time consuming and we have big (wo)manpower problems.
In any case, if you think the bug is very important and should be in the Debian BTS, you can report it in Debian as well as reporting it to KDE. Make sure you mention the KDE bug in the Debian bug.
Third case: your problem is not a bug, just a feature request.
Until now, I have talked about bugs, when you find something that is clearly not working right in your system. But what about when you want to ask for a new feature in a piece of software?
In very few cases this belongs in a Debian wish list. Most feature requests apply upstream and you should tell the about your idea. If you do not tell them, it is unlikely they will implement it. Still, after reporting, you should accept it if upstream thinks it is not a good idea or it is not interested enough to implement it.
Post updated on the 30th September, thanks to Rupert Swarbrick for grammar fixes.