Here are a couple tips. First, don't search if it has already been done for you.
Use the list of related questions in the sidebar. If a question is asked enough, the related list is sure to include some duplicates.
Use the suggested duplicates from the close/flag windows. If you click Flag > It doesn't belong here > Exact duplicate, (or Close > Exact duplicate) there is a list of possible duplicates which have been frequently linked or used as a duplicate close reason.
If these lists don't provide a good duplicate, use the Advanced Super Ninja Search Options. These will help you filter bad duplicates out of the search results. For example:
- A good duplicate will have an accepted answer.
- It will usually have a decent number of upvotes.
- It will probably not be closed.
- The title will contain some key words. These may show up in the body of other, non-duplicate questions, so narrow your search by requiring them in the title.
Note that the number of upvotes on the answer is more relevant than the number of upvotes on the question, but the closed and title search options only work for questions, so you may need to run two searches. It would be nice if those options worked on the question containing an answer too.
Example Searches:
Accepted answers in the MySQL tag with at least 10 upvotes which contain the phrase "group by": [mysql] "group by" votes:10 isaccepted:1 is:answer
Unclosed questions with an accepted answer in the MySQL tag that have the phrase "group by" in the title: [mysql] closed:0 hasaccepted:1 is:question title:"group by"
