The best way to ensure you get sharp images is to hold your camera in a way that you support it and your body acts like a tripod. Body stance is an important part of this. While standing up straight, not leaning towards the subject, your feet should be shoulder-distance apart, and your knees slightly bent. Like the classic athletic position.
I used to hold my camera like this and wondered why my handheld images weren't sharp.
The elbows are out, and this doesn't provide the camera much support.
Here's the best way to hold the camera. Elbows pressed tight against the body, hands tightly gripping the camera and the lens. The left hand in this image is directly under the camera lens providing support. Both hands are pushing the camera into the photographer's face.
Now that I hold my camera like this, I get more sharp images when handholding.
Here's my old way of shooting verticals.
One elbow moves up, and the camera isn't stable. I refer to this as one elbow flapping in the wind, not giving any support to the camera and lens.
Here's the best way to hold a camera for a vertical shot. Elbows in, arms tight against the body, tight grip on the camera and lens, and camera pressed against the face of the photographer.
The longer the lens, (think 70 to 200 zoom or 100 to 400mm zoom), the further you need to move your supporting hand out towards the end of the lens. Now that I hold my camera and lens using these methods, I've increased the number of sharp, usable images.