The bac has pretty well covered what has to be done. Another thing to remember is that your camera has to be still when taking your photo. Several of your samples, where you blame the camera for being blurry, are really camera motion.
When you are using flash, please keep in mind that there is indeed a range (10 to 12 feet) that is too far. However, there is also a range that is too close and that results in over exposure. Try to stay at least 6 to 7 feet away from your subjects.
If you are going to mix higher ISO settings with flash, as the bac suggested, it may take some experimenting to prevent overexposure (bleached out looking photos).