The fire elemental meditation is one of great power. However, if performed improperly, it can be detrimentally dangerous. Make sure you follow these instructions exactly as they are written.
First, get yourself into a trance. Instructions on how to do this can be found in my article, How To: Induce a Trance. Once you have induced your state of trance, you are ready to perform the fire elemental meditation.
To begin, feel your skin becoming warmer and warmer, to the point that you feel if someone were to touch you, they would get burned.
Next, starting with your root chakra, light it on fire and make it hotter and hotter until the chakra is burning like the Sun. Do this for the sacral, solar plexus, and throat chakras. When you arrive at the solar plexus chakra, on top of making it blaze with fire, visualize and will a brazier to keep the flame alive.
Do not, under any circumstances, set aflame the heart, 6th, or crown chakras. Doing so can cause drastic and detrimental effects, which, sometimes, can be fatal.