A. The conventional strategy is to withdraw money from your taxable accounts first (as they are usually taxed at long term capital gain tax rates), then tax-deferred accounts such as traditional IRAs and 401k (this will be subject to income tax rates), and finally Roth IRA (so the tax-free money has more time to grow).
However, if the bulk of your assets are in 401k or traditional IRA accounts, since these accounts face RMD requirements from IRS and a large withdrawal after age 70.5 could bump you into much higher tax brackets, you need to start reducing future RMDs by withdrawing money out of those accounts while still in lower tax brackets. If you don't need such money, you can convert them into Roth IRA.