Could you possibly get away with using one of the automatic sharpening tools? Yes, sometimes, of course you could. And no harm would be done.
But (like our discussion of Levels above) this is one of those adjustments that is ALWAYS better when you do it yourself.
So, always use Unsharp Mask ... PLEASE!
Don't ask me why every digital image needs to be sharpened (except, of course, those that are intentionally "soft focus" for whatever reason). But they do.
The key points are to zoom in on the image so that you're seeing it 100%. In other words, the size of the print you hope to make. And be sure to have the Preview box checked so that you can see the effect not only in the little magnified box but also in the larger image itself.
Hold the mouse button down and drag the image around so that you can look at several areas before making you final choice. Choose a setting that is lower than you might expect, but high enough to have some real effect.
It's a learned process; practice, practice, practice.
And finally, after you've accepted the adjustment, look at the image once again to be sure it's what you want.
Oh ...and one last (sad) point: NO AMOUNT of sharpening, will rescue a badly out of focus image. Sorry!