At this point, we've all been on StackOverflow somewhere between 100 and 10,000 times and you've probably noticed some not-so-nice comments in response to someone's question: "OP needs to be more specific", "I hate when n00bs ask vague questions", etc. Here are a few things to keep in mind before posting your question on the forums:
Research!
Try to do as much research as you can on your own before going to the community for help. On some occasions, someone may have a perfect link that you couldn't find, but often times you can find the answer you are looking for if you ask Google a better question.
Be specific
Try to give as much context as you can so that others know what problem you are trying to solve. When possible, also post your code so others can quickly identify if there's a problem and will suggest a fix.
Post Like a Developer
That is, speak the language. If you don't know the language, research it. In fact, doing this research may help you solve your problem without going to the forums. Instead of asking "How do I add something to list?", you should be asking "How do I add an element to an array in Ruby?".
Write Like a Human
These are humans answering your question, after all. Make sure you proof-read your content for spelling, punctuation, readability, specificity and, most importantly, that the question you are asking will get your problem solved. In addition to this, think about future scenarios where someone may have this exact same problem. Google indexes everything on these forums, so make sure you're doing a good job of making it easy for someone to come across this thread in the future!