I'm sure people who have done this will give you a better answer but here is the basics for someone who will be living 100% off of investments before they are of retirement age:
Years 1-5: begin living off of your taxable accounts and Roth contributions (if you have them). Your withdrawal rate will likely be much greater than 4% on your taxable account--that's okay because you're getting your other monies ready.
Years 1-5: begin rolling over from traditional IRAs to Roth IRAs. You will pay taxes on this conversion. If you live on a low budget (say 25k/yr) you will pay very modest taxes on this roll over.
Year 6-death: You can begin withdrawing your entire rollover amount from 5 years previous.
So in practice (ignoring investment gains/losses/inflation/taxes)
Person with $750,000 nest egg. $125,000 in a taxable account. $625,000 in IRAs. 25k/yr budget:
Year 1: withdraw $25,000 from taxable account. Roll $25,000 from IRA to Roth IRA.
End of Year 1: $100,000 in Taxable, $600,000 in IRA, $25,000 in Rollover Roth IRA
This * 5
Year 5: withdraw $25,000 from taxable account, rollover $25,000 from IRA to Roth IRA
End of Year 5: $0 in taxable account, $500,000 in IRA, $125,000 in Rollover Roth IRA of which $25,000 is eligible to withdraw without penalty (as it has marinated for 5 years in the Rollover Roth IRA)