Be clear. If it is hard to understand your writing or the specific question you have, it's a bad question. This is the first and most important criteria all questions should be judged by. The merit of the question itself is not apparent unless I can understand it. Use proper, clear English and bold important points to help readers follow your meaning.
Remember you're phrasing a question for experts. Write your question as if you're expecting a professional to read it. You don't have to make it knee-deep in jargon, but be respectful and concise. Read your question yourself aloud to get a feel of how clear and logical it is.
Do your homework. If you want to know what a Saccade is, take a moment to Google/Wiki search the term. Ask a specific question and give some evidence that you understand what you're asking about. If it looks like you're just asking us instead of asking Google we're not inclined to answer you.
Don't Expect Mindreaders. Just because you did your homework doesn't mean we know that. Tell us what you know about your question, tell us why you're asking. If your question has no motivation we might suspect it's not a real question. Don't get mad when people ask for clarification, and instead avoid that by providing clarity from the start.
Be specific. Answers should be answers, not books, novellas or discussions. Questions aren't so we can tell you the whole history of a term or concept, but rather how X concept interacts with Y, ect. Your question doesn't have to have a Yes or No answer, but it should have an answer.