Install outlets (receptacles) with the ground hole either up or down. Both are correct. But be consistent.
By the DIY experts of The Family Handyman Magazine:December / January 2008
The electrical code allows outlets to be installed with the ground plug hole facing up, down or sideways. It's up to you.
The ground hole is in the down.
You usually see outlets installed with the ground hole down (Photo 2). But it's no better than installing them the opposite direction (Photo 1). Electricians endlessly debate this and vigorously exalt the virtues of installing it one way or the other, but we'll tell it to you straight—it just doesn't matter. Both ways are correct. The electric code doesn't specify which direction the ground plug hole needs to face. One way isn't safer than the other—as long as the outlet is wired correctly.
It all comes down to aesthetics, so install them whatever way looks best to you. Incidentally, the ground plug is typically down in the United States, the opposite of how it's generally installed in Canada.
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.