Image Stabiliser. Use a tripod for shots over 1-3 seconds since your hands cant maintain their steadyness for that long.
Of course, other than that you can perch yourself against something for support but effectiveness depend on user itself.
The general rule of thumb to safely expose a sharp image handheld is not to shoot with a shutter speed slower than 1/focal length of the lens. Example, If you are using a 50mm lens, don't shoot with shutter speed slower than 1/50. If u need to go beyond that usually what I do is leaning to a wall or something to stable yourself, breath in and hold, and shoot! Good luck trying!
If you try your hands with a high end setup (Pro Body + Pro Lense + Flash) for one whole day, you'll see why usually at the end of the day, most users of these setups have a tired wrist. =) It's easily 3 KG