Here are a few ideas:
Always prepare or have prepared financial statements on a comparative basis. This allows you to spot overhead items that appear to be out of line. Go down every overhead category line by line to spot overhead increases, then investigate.
If you review practice overhead, be sure to have access to a year-to-date, detailed general ledger. This type of general ledger lists all financial activity, including journal entries, for each general ledger account for each month of the year to-date. This is an excellent tool to use when analyzing the appropriateness of specific overhead categories. This type of report allows you to see if, in fact, entries to the account are realistic, necessary, or even misposted.