The IRS recommends getting Publication 334, Tax Guide for Small Business, for advice.
Nonbusiness taxpayers can control income sometimes through sale of investments to generate gains or take losses, and in this year, there are plenty of stock-market losses to go around.
The book on that is Publication 550, Investment Income and Expenses. The deadline for any of those deals is Dec. 31.
If you’re doing taxes next year and want a last-minute way to pull down the total, make contributions to an Individual Retirement Arrangement, or IRA. That can be done right up to the day tax returns must be filed.