.....good tips all, but some things work for some that don't for others....leaning against something usually works awfully well, like a wall, or street light, or building, your car, or whatever....but when that option is not available, I jab my left elbow just to the left side of the solar plexus, (just below where the bottom rib bones meet in the middle), the right elbow just to the other side of the solar plexus, pushing in also, the left hand holds the bottom of the camera and is by far more of a tripod than the right....the right hand holds the right side of the camera where the controls are, mainly on top, and works the controls.....
.....then, what I do, is keep barely pushing that shutter button to ensure focus as I breath deep and exhale a couple of times....then I inhale full and hold it, while sorta' releasing my shoulders to sit on a beach ball named lungs....I barely push the shutter button one last time holding the focus, and stare at something in the picture while pushing on down with the shutter button, looking for that something stared at to come back....you'd be amazed at some shots you can get under 1/60th with nothing to lean against.....
.....here's some shots from a show one night in a small theater in coastal Mississippi where no flashes were allowed....I was leaning against a large pillar that held up the balcony, or these probably wouldn't have been possible....every one of these shots was at least 1/8 sec with some 1/4 secs mixed in, and you can only hope to get lucky without something to lean against with exposures that long....was using a Canon EOS system at the time....pictures to follow so you can read this one easier.....