If you are using an SLR, get a rubber eyecup for the eye piece and press it against your eye/forehead to form a triangle with your left hand underneath the lens and the right hand on the grip/shutter release. Tug your elbows in towards your body as firefox mentioned. "Roll" your finger over the shutter release button instead of poking it down. Hope that helps.
Additionally, if using compact digital cameras, try using the optical viewfinder/EVF instead of the LCD. You can handhold it better that way. Take a deep breath before gently squeezing the shutter button.
lean ur back against a soild wall or support.. cam on ur left shoulder, lens pointing to the left.. tilt head to look into viewfinder.. for additional stability put ur left hand on ur waist.. in other words ur shoulder is supporting the cam la... funny position but it works for me
Please note that the methods mentioned above are only compromise and cannot replace the use of a tripod(good quality ones) if situation allows. If you can get a remote shutter release, so much the better. If you can't use the self timer.
This method seems to work well if I dont have my tripod around.
1) Use the LCD to compose the pic,
2) neck strap around your neck
3) both arms holding cam, stretch out until the neck strap is taut.
4) Lock the focus (half shutter)
5) Release all air from lungs
I found this tip somewhere on the web but cant remember:
Add to the above, a string tied to a nut that screws into the tripod mount. The string should be long enough to reach your shoes with surplus.
1) Attach the nut
2) Step on the string
3) Hold cam with slight upwards force til taut
4) Same as above 4-6