Officially it's the "Audit Techniques Guide," not to be confused with the Internal Revenue Manual.

https://www.irs.gov/pub/irs-utl/attorneys_atg.pdf

Here's what I do, and why.  All deposits to the lawyer's bank account are reported as gross receipts, Line 1 of Schedule C.  This does not include payments to the attorney's trust account, which are generally refundable retainers.  When the money is transferred from the trust account as the work is billed, then it goes into gross receipts.  

Client costs (which include court filing fees, and sometimes other types of expenses, like expert witness fees, depending on what type of cases the lawyer handles) are deducted as other COGS.  This lowers the gross income on Line 7, and lowers the ratio of expenses to gross income.  Call me superstitious, but I believe the higher the gross income, and the higher the ratio of expenses to gross, the more likely an audit.

It's also important to have all the gross receipts on Line 1, even those that are client costs, because lawyers are 1099'd more than other professions (except maybe for those practicing medicine).  IRS will want to match total 1099's to Line 1.  Even if they don't do that, the first thing an auditor will do is match bank deposits to Line 1.