Check your focus with live view.
If your camera has live view, press the live view button to bring the live view up on the screen. Then simply twist the ring to focus the camera.
Zoom in to check fine focus.
Tap on the live view zoom button (often a small magnifying glass) to zoom into the image.
Zoom in and focus past the subject, then pull the focus back.
When you’re checking your focus, it’s worth focusing past the subject, then pulling the focus back, just to make sure it’s as sharp as possible!