There are several things you can do to improve your chances of getting sharper images.
On most SLRs, and some of the mirror-less or four thirds cameras, there is an option of selecting what point it uses to focus. Meaning, when you look through the camera and see some flashing dots or squares (or something similar to the image on the right), those are your focus zones or spots. Make sure it is NOT set for the camera selecting which of those spots are targeted for focusing. When the camera chooses where to focus it can often pick the wrong thing. If you have a subject that is behind something in the foreground the camera will usually pick the closest object, which is not your intention, and you’ll end up with the wrong thing in focus. Find the setting that allows you to adjust which target focus zone the camera uses to focus. Depending on the camera make and model, that can usually be adjusted with a dial or joy stick on the back of the camera, while you are looking through the view finder. This frees you to choose the most appropriate zone or spot for your subject or scene.
Having that crystal, sharp image can be hard to catch. But with a little know how and direction, those slightly blurred faces can become so sharp and clear...you may be amazed at your own skill. And the simplest way is to use a tripod and trigger release, but do not worry. The majority of us are just carrying around our SLR without the extra, use a ledge or flat surface instead.