For Sole Proprietors

The first link below opens a .pdf document that outlines the various income and expense categories that are reported on a Schedule C and discusses what record keeping is required. This document makes several references to the following companion Excel spreadsheets that can be downloaded and used to track your own income and expenses.

Overview of Sole Proprietor Record Keeping
Schedule C spreadsheet (2020 Excel format)
Schedule C spreadsheet (2020 Numbers format)

You can find per diem rates to use in lieu of actual meal & incidental business expenses here:

Other forms that you might like to review:

Schedule C – Profit or Loss From Business
Instructions for Schedule C
Schedule SE – Self Employment Tax
Form 8829 – Expenses for Business Use of Your Home