Congratulations! Hopefully you've done enough planning in your working years, and by this point you've got it all figured out. But if not, you've got quite a few decisions to make.
Start by figuring out what type of lifestyle you want in retirement, and how much money you think it might cost you. Create a retirement budget that includes everything from essentials like food, utilities and housing costs to the nonessentials that make life more enjoyable, such as travel and entertainment. And don't forget that you'll undoubtedly run into unexpected expenses - medical bills that aren't covered by Medicare, a roof that needs fixing or a car that's got to be replaced - and that your living costs are likely to rise along with inflation over the years.
From here, you'll need to figure out how much money you should be withdrawing, and which accounts to tap first. You'll also want to look into collecting social security payments. You've also got some decisions to make about your home. Do you plan to relocate? Downsize to a smaller home?
If you don't think you'll have enough to sustain the lifestyle you want, you may have to consider other options like scaling back your retirement plans, taping your home equity for income, working in retirement, or even delaying your retirement by a few years.