In general, please ask only one question per thread, unless your questions are closely related.
Similarly, if your question is answered and you then have a new, unrelated question, please post it in a new thread and do not add it to your existing thread.
Each thread should be for a specific question or topic and not a place for you to make a personal "help me and only me" mini-forum. 
In a nutshell, one question per thread makes it quicker and easier for other people to find answers by browsing and searching the forums. It also makes it easier for people to answer your questions which in turn means your questions will be answered more quickly.
Here are the arguments in more detail, in case you are not yet convinced:
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Multi-question threads make searching more difficult and time consuming. If they appear in someone's search results (which is more likely the more topics they include) then the person has to read the whole thread to see if it's relevant, and if it actually has an answer to the one question they care about, before moving on to the next search result.
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Multi-question threads are difficult to read at a later date because unrelated questions, answers and follow-up questions are interwoven.
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Multi-question threads are an annoyance to people keeping an eye on them for replies. Another person reading the forums may be interested in one of the questions but is unlikely to be interested in all of them. That person will have to read every reply to the thread to see what it's about. Compare this to single-question threads where people can keep an eye on those which interest them, knowing that all replies are probably worth reading, while completely ignoring those which do not.
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Multi-question threads almost always have useless descriptions which might as well just say "Help!" or "Opus", since it is rarely possible to summarise several questions in one subject line.
This gives people browsing the forum for new messages the choice of completely ignoring the thread because it has no immediate interest to them, or of reading it just in case it is interesting. Guess which option most people choose...
(Of course, poorly chosen subjects are a problem in themselves and are not unique to multi-question threads.)
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Multi-question threads are difficult to answer because people trying to help have to work out which questions still need attention and which are resolved. Doing so often requires re-reading the entire thread, complex and interwoven as it is, and making a mental note of which questions still need answers.
This also means some of your questions may never get an answer if people don't notice that the thread still has outstanding issues within it.
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Multi-question threads will often be left unanswered for far longer than if the same questions had been posted in separate threads. This is because those responding generally want to respond to everything in a thread at once, to avoid the problems discussed above, and will not respond at all until they have the time to do so.
If questions are in separate threads then people can answer them one at a time, as they find pockets of spare time, and trivial questions can be answered immediately, in passing, while more difficult questions can be left until later (using the forum's bookmark thread feature, or normal browser bookmarks, to keep track of them).
If multiple questions are posted in a single thread then people probably will not respond to it until they find the time and energy to think about, investigate and answer every single question in a single reply.
Additionally, multi-question threads offer no big advantages to offset the very real disadvantages above.
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They mean there are fewer threads on the forum but the forum is already very busy with thousands of threads. Nobody cares if the forum has 5000 threads or 5010.
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They mean the poster only has to come back to check one thread, but checking (or subscribing to) more than one thread isn't difficult or time consuming, and the poster will probably get answers quicker if they post one question per thread.
Of course, if the questions are all closely related then it does often make sense to post them in one thread. Asking what is essentially the same question in multiple threads is not helpful and makes finding relevant replies difficult as well. There is no absolute rule about when you should split questions into multiple threads, but you usually should. Please consider the points above before making your post.
Thanks!