To start with, when writing a query, whether online or via a paper letter, think about what you have just written. Seeing the sentence, "please send me everything that you have about . . . " guarantees a reply that is not going to be what you just asked for. A person may have 500 pages of paper of handwritten notes, or 1300 pages of transcribed church records (I know of one person who has that, and sells copies of pages for one dollar a copy. More power to her). Would you copy a great deal of information and send it off cost free to someone whom you have just met over the internet or via a first letter? I didn't think so.
A library is in the same situation. It is not unusual to have a limit of 15 to 30 minutes that a staff member can spend on the research for a question. Everyone is entitled to the same service so taking hours or days to assist a single patron is not an option,. Neither is going through every census, every newspaper clipping (and land records, will papers, or probates are often not in the library let alone in the same building). What if the copy charge is ten dollars a copy, such as our organization charges? Want a thousand dollar invoice?
Asking for something like "need information on John Smith and his wife Mary (any clues all about her name? Children?) who moved to Kansas (where?) in the 1800's (good - that narrows it down to 100 years) and built a house" is not focused. Did they buy land? Where? For how long?
In other words, it's OK that the asker doesn't know these items and is requesting help. But if you can supply more identifying data, then do so.
My personal favorite is "Researching John Schmit from Barvaria or Burlin Germany sometime in the 1700s or 1800s." Please, folks, take the time to learn how to spell Bavaria (Bayern) or Berlin, and please have a better idea than a two hundred year time span.
One also frequently sees a question on a message board, a list, or a Usenet newsgroup, along the lines of "Where's the Black Forest?" Other than the quick answer of "in a group of trees," questioners are advised to use their computer to do a quick search engine lookup for, in this case, Black Forest and map, and see the results. Don't be lazy. Experienced researchers get frustrated helping folks, and Germans as a rule are quite direct in suggesting that other folks learn to do a little research and not be either lazy of insular.
The watchwords here are to think through the question and give as much information as you have, including dates and places; use the web to see if there is a mention of a place and its location; and ask for direction on how to find a class of records (how to find information Germans from Russia, rather than information about Germans OR Russia). Helpers like to help. Give them a little information to help them focus in on a specific task. Being a newbie is not shameful--we all are at some time. Ask, don't demand. Speak in your emails as you would to a person in front of you.