On a big project that I maintain since a few years, we have several combined indexes to fit various needs, thus SQL commands which need to perform the result immediately. So, from the SSMS execution plan, with the way the INNER JOINs are being constructed, the fields in the WHERE clause and the list of selected fields, we came up with what was necessary to obtain that result.

However, this raises a concern as to know if it wouldn't have been simpler to simply build one index with all the fields of the table. Or, is the way we have done it by adapting the application based on various SQL commands here and there to include the related indexes was the way to go.