Retiring next week. Should withdrawals be made first from a post tax account (i.e. Roth IRA) until its at zero and then go to pre-tax withdrawals (conventional IRA) ?
This depends on your circumstances, but I would lay off the Roth until you are forced to raid it.
Walkinwood posted an article about this topic today.
Aside from leaving the Roth undisturbed, you have pre-tax funds, taxable accounts, and (eventually) social security. IMO there is a lot of bad advice around on these topics. Factors are married or not, amount in various accounts, cash needs and other income, and SS payments at various ages.
The article cited suggests withdrawing pretax funds first (IRA, 401K, etc.)provided you have reached age 59 1/2, putting off SS until age 70 (especially if you are married or female, and leaving post tax funds and Roths alone.
If you are below 59 1/2, there are various fancy withdrawal ideas, I think one called 72T. These are discussed from time to time around here