After reading several of the other blogs and their letters, it looks like most of them actually have an idea on how to write a letter to ask a question or find information.
Why is letter writing important to me? I am one of many volunteers that get to answer queries from other genealogists and while most come by E-Mail, I still get many letters.
When I took a beginning genealogy course years ago, one session was on writing queries. The instructor passed out Everton Genealogical Helpers and they had page after page of queries that people paid Evertons to publish. Since there were hundreds of queries you could see which ones were good queries and those that probably never got an answer. You know the type "I am looking for the parents of Thomas Kelly born 1825 in Kentucky".
Today you can check any Message Board or Mail List on RootsWeb and get the same education. Which queries get an answer? Which never get an answer?
Try to help out the volunteers, let them know what you have already found so they do not have to go through the same search you have already done. A few days ago I got a query asking to find the birth dates for five children of a couple I had not researched before. While we have quite a few birth records, where do I start? 1890s, 1920s, 1940s, etc. I found two birth dates, and he said that confirmed those two dates, but nothing on the other three.
If you know nothing about the people your query is on let the volunteer know that also.
Good queries bring good answers, so check out how to write a good query.