As a newbie to the Raspberry Pi and electronics in general, I would like to start hacking around with the GPIO pins but any tutorial around the Internet warn me about frying the Pi one way or the other. I would like to know what are the bare minimum precautions and safety measures to be taken while using the GPIO pins so that I can reduce the chances that I would fry the Pi. I have taken a look at the GPIO documentations on the RPi site (http://www.raspberrypi.org/documentation/usage/gpio/). The only thing mentioned was
If you follow the instructions, then messing about with the GPIO is safe and fun. Randomly plugging wires and power sources into your Pi, however, may kill it. Bad things can also happen if you try to connect things to your Pi that use a lot of power; LEDs are fine, motors are not.
In that case, what would be the things NOT to connect to the RPi and what are the possible "bad things" that can happen?