Basically it comes down to balance. Include some basic information, but not too much (No one is going to read 4 paragraphs of background anyway).
Ask specific questions, but not too specific, and about a common area or topic, and under the appropriate subject heading (Though I imagine most long time participants on here look at questions in the "All Topics" mode anyway) It is also OK to ask two or three related questions, but not ten. Start basic, ask for clarification or follow up as needed. If you have a completely different question or thought mid topic, start a new thread.
It is a good idea to do a quick search of the topics before you ask a question, but I get it, your question is unique. However, the search feature on here is not that great, a search on "Where to stay in London" turns up a couple thousand hits, but the two topics started in the last couple days do not show as most recent, puzzling.
If asking about visiting a country, include the time of year you are thinking, maybe the activities planned, and at least the rough amount of time allowed. It might also be good to hint at where you are from, though it is assumed you are from the US.
If asking about hotels or restaurants, I am less concerned about trying to specify a budget, it is OK to collect names, then off to investigate. If someone suggests a $$$$ hotel, and others a $ hotel, it is up to you to decide, even the $$$$ hotel might be had for $$ for your trip. Of course I rarely/almost never give Hotel recommendations, just too many different expectations. A restaurant, maybe.
If you get responses, check back, answer any questions that might have been asked for more info, maybe let people know what your thinking is given the input provided. I do not think there is a need to acknowledge each response, or thank people multiple times, that detracts from the core topic, and makes reading the thread clunky for others looking for similar info. If the responses surpass 15 or 20, indicate that you have the info and consider the thread done. Personally I avoid any thread with 30 or 40 responses, by then there is usually lots of good information, but also plenty of bad, and likely also off topic.
It is also nice to stir things up. Refer to immigration as "customs", everyone knows what you mean, but some rarely contribute except to point out the differences. If you are clever, you can find a number of these triggers (Schengen, EITAS,...) We are here to have fun after all.