When you open a new homework thread, you are asking volunteers to spend their time to help you, so spend a little of your time to make their job easier. Effective communication is the key, so keep these general considerations in mind when you make a new thread:
We're not in your class; we don't know what's in your notes; we don't know what you've tried; and we can't read your mind. All we have to go on is what you write.
We don't really know you. If it's not obvious from the question, let us know your level of knowledge so that we can reply on an appropriate level.
The guidelines below will help you avoid some common obstacles to getting help. (Many of the points are, in fact, part of the forum rules, and as such, they're not really suggestions or advice. You're supposed to be following them already!)
Use the homework template.
This is primarily to make your post clearer to the homework helpers, but it's also there to help you. It is never a bad idea to structure your work (here and in general), and sometimes organizing your thoughts can help you clear up your confusion on your own. Also, if you don't have enough to fill out the template, it's a sign you shouldn't be posting yet.
Reproduce the problem statement accurately.
It's very frustrating trying to help a student with a problem only to discover that he or she omitted important information.
Ideally, type the problem statement exactly as worded. You're probably not the best arbiter of what's important and what's not, so include everything. If you decide to paraphrase or summarize anyway, make sure you're not accidentally changing the meaning or omitting important information. If you're only asking about one part of a long problem, it may not be necessary to type up the entire problem, but you need to ensure you've provided the proper context for the sub-problem.
Show us that you've thought about the problem.
The forum rules require that you show an attempt at solving the problem on your own. Obviously, one reason we want to see your work is because we prefer to help those who are genuinely trying and interested in learning. What's more important is that we need to see what you've tried so we know how to help you. For your attempt, you can offer a partial solution to the problem, but you don't always have to. What we're really interested in is seeing what you're thinking so we can identify and clear up any misconceptions or points of confusion.
Here are some common mistakes to avoid:
Don't simply say "I have no clue," "I have no idea where to start," or "I'm completely lost." These don't qualify as attempts. Instead, it suggests you haven't put much effort into reading and understanding your textbook and lecture notes, going over similar examples, etc. The helpers aren't here to answer your questions so you don't have to read your book.
Don't simply say "I tried for hours and didn't get anywhere." This is really no better than saying "I have no clue." It tells us absolutely nothing about where you're getting stuck. If you tried for hours, you must have had some thoughts about the problem. What were they? Show us what you tried, explain why you think it was wrong, and so on. Better yet, identify what's confusing you and ask specific questions to help you figure things out.
Don't just give a vague or general description of what you tried. If the problem lies in the execution, as it often does, we can't help you find mistakes without seeing your work in detail. Even if you provide your final result, it usually does little to help us figure out where your attempt went awry.
Do not simply post images of the problem statement or your work.
While posting images may be convenient for you, it's actually one of the most effective ways of getting your request for help ignored. Images are often too big, too small, rotated, upside down, out of focus, dimly lit, or of otherwise poor quality, and your handwriting probably isn't as easy to read as you think it is. Images are a hindrance to the helpers as portions of the problem statement or your work can't easily be quoted. Using images also doesn't qualify as filling out the homework template, so your post may be deleted.
So type up the problem statement and your work. Think "If I can't be bothered to spend my time typing it, why should they be bothered to spend their time reading it?" Use scans or photos for supporting figures. You may, of course, attach an image of the problem statement in addition to the typed version; in fact, if it's a complicated or long problem, you probably should. But you should always provide a typed version as well.
When you do use an image to your post, make sure it's in focus, oriented the right way, well lit, etc. It seems like this should be obvious, but experience has shown that people frequently post incredibly poor images. Add it as an attachment to the post. Don't host it externally. That way it will remain on PF indefinitely, and your thread will remain useful to future visitors.
Format your post to make it easy to read and follow.
You're more likely to get responses if prospective helpers don't have to decipher what you wrote.
Use paragraphs and separate them with blank lines. Take advantage of the typesetting features in xenForo. Use LaTeX for mathematics. There's a good tutorial on LaTeX here.
Follow standard conventions when writing mathematical expressions. In particular, use parentheses where necessary. Don't make us have to guess what you really meant to say.
Don't use large, bold, or colored type to draw attention to your question. We can read the normal font just fine.
Use proper English.
Grammatical and spelling errors littering a post can be quite distracting and make it hard to read, and in the worst case, these errors can obscure the meaning of what you wanted to say. You're more likely to get responses when your post is well written.
Use proper grammatical structure, punctuation, capitalization, and spelling to express your ideas as clearly as possible and to maintain the quality of the posts on the forum. In particular, avoid the use of txt-speak, which many of us find grating. Physics Forums isn't your cell phone.
Despite your best efforts, a few mistakes may slip through — a typo here, a missing tag there. It never hurts to check over what you wrote for errors and to fix them. It's a good habit to get into in general.
Preview your post before submitting it. Find obvious errors and fix them.
After you submit your post, reread it one more time in its entirety to see it makes sense as a whole, especially if you did a lot of editing while composing your post. Make sure it looks the way you expect. Fix broken tags, broken links, etc. Delete extra copies of the template.
If you find mistakes, click on the Edit button which appears in the bottom right corner of your post. The ability to edit a post is temporary, so don't put it off. Avoid replying to your own post with corrections because some helpers will skip over your thread when it looks like someone has already replied.