Sleep On It
Always wait at least one day between writing your query letter and dropping it in the mail. This gives you a mental break and allows you to look at your query with fresh eyes and a fresh viewpoint.
You might come up with a better lead or a more effective approach altogether. You may discover that the tone of your query isn't quite right, or that your attempt at humor has fallen flat. Of course, you also might discover that the query is better than you thought it was when you were struggling to compose it.
The Mind's Editor
A read-through 24 hours later also might reveal typos or missing or extra words that you just didn't see the first time around. By giving yourself a waiting period, you can correct any errors before you send your query off. Remember, you're hoping to impress an agent or editor with your writing ability, and careless errors will only tarnish your image. While most people will overlook minor goofs, you owe it to yourself and your writing career to make your query the best it can be, both in concept and in mechanics.
When we read our own copy, and especially when we read the same thing several times, our brains can act like editors, transmitting what we meant to write rather than what we actually typed. As we hone and polish our query letters, we might insert different words but fail to delete the original words. Sometimes we misspell a word, or make a grammatical error that we don't catch at the time.
But because we know what we wanted to say, our eyes sometimes just skip over these mistakes. That's why a final read-through, preferably after you've taken a good, long break from working on your query, is critical; you're more likely to catch those kinds of mistakes after a rest.
Alert
Friends or relatives who are unfamiliar with the way agents and editors work might urge you to include much more detail in your query than is warranted. The goal of a query is to pique an agent or editor's interest so he will invite you to submit your proposal, and your proposal is the proper place for those details.
A Second Opinion
If you have a friend or relative who is willing to critique your query and whose judgment you respect, you might ask for her input. This can be especially valuable if you're concerned about whether you've made your query sufficiently clear or interesting.
Ideally, a friend or relative who reads your query will understand the broad outlines of your proposal and will be interested in learning more; that's the reaction you want from an agent or editor, too. A second set of eyes also can help identify typos and other errors in your query.
If you use this technique, don't give the reader any extra information about your manuscript or book idea. Your query letter has to stand on its own; you won't be there in person to fill in the blanks when the agent or editor reads it. Again, the fact that you know what you meant to say doesn't necessarily mean you did a good job of explaining it on paper, and the outside reader can give you valuable feedback on that point.

