How to respond on your blog to a question from an outsider.
There is nothing more valuable than when others take the time to post to your blog. Honor that investment by responding with a thorough answer when it happens. A question from an outsider, coupled with a valuable answer is exactly the kind of magnet for people looking for an answer to a similar question in the future.
I've often gone searching for an answer in Google only to be pointed to someone's blog where the answer was thoroughly answered. For example, if I search for "how to create a table in Microsoft Word" in Google, one of the results (with a PageRank of 4 by the way) on the first page told me exactly how to do it.
If there is a spelling mistake or grammatical error in the question, consider fixing that also. Good spelling and grammar are more likely to be used to search later than exact misspellings.