As a word of caution, keep in mind that withdrawals from retirement accounts that have RMD requirements are considered taxable income.
Here's where this can get you into trouble. Let's say that you'll turn 70 1/2 in 2018. This means that you have until April 1, 2019 to take your first RMD. However, your second RMD will also be due by the end of 2019. By waiting until 2019 to take your first RMD, you'll have two big withdrawals in the same calendar year, which could easily bump you into a higher tax bracket.
The point: If you turn 70 1/2 during 2018, it can be a smart tax move to take your first RMD by the end of the year, even though you aren't required to do so.