Instructions in parenthesis might not be necessary.
Generate a Table with an Empty Equation
Insert → Table → Select 3 columns and 1 rows.
Select the whole table, right click, Properties.
→ (Preferred width: 100%.)
→ Borders and Shading… → None → OK.
→ (Options… → Automatically resize to fit contents → OK.)
Cell tab → Center
(You can create a paragraph style for the tables that include equations.) Center the text of the middle cell. Right align the text of the right cell. (Alternatively, you use a paragraph style for center-aligned cells and another for right-aligned cells. I use these styles, along with another for left-aligned cells, for all my tables.)
Place the cursor in the middle cell.
Insert → Equation.
Some people add an extra step: set column width of the columns to, for example, 10%, 80% and 10%. This is unnecessary because the middle column expands equally to left and right when the equations is sufficiently wide, thus keeping the equation centered. (If you want to make more space wide equations and you are willing to sacrifice a little bit of centering you can use a two-column table. In this case will need to assign percentages).
To create new equations with as a keyboard shortcut, go to File → Options → Customize Ribbon → Customize Shortcuts and then selecting "Building Blocks". Search for your newly created equation template in the right list, then assign a keyboard shortcut to it.