The two main reasons a tripod is steadier than a person are that a tripod has three legs and it doesn't breathe. So it stands to reason that capturing steady images without a tripod is best accomplished by either removing the camera from your shoulder or finding a totally stable object to brace yourself against.
Trees, light poles, and buildings all provide a solid vertical support that you can lean against with the camera on your shoulder. The greatest stability is achieved by either leaning to the right, trapping the camera between your head and the support, or by embracing the support and leaning against it while making the shot. (Note: This technique only works with poles and small trees.)
Horizontal support--surfaces upon which you can rest your elbows--in the form of automobile hoods, tables, fences, and even chair backs, is available practically everywhere. Shooting a quick sit down interview without a tripod is much steadier if you either kneel and place your elbows on the subject's desk or sit backwards on a chair so your arms can rest atop its back support.
When shooting off the shoulder, use a commercially available or homemade bean bag to support the camera. The bean bag allows the camera to be steadied on uneven surfaces as well as precise vertical framing that is otherwise difficult when the camera is placed upon the ground or another flat surface.
