For pronounciation, keep in mind that:
the "A" is pronounced as in "ah,"
the "M" is pronounced as "mng."

Do a meditation for 7 - 10 breaths. Chant the sound several times each breath (for example three times).

Open the Root Chakra

Let the tips of your thumb and index finger touch.
Concentrate on the Root chakra at the spot in between the genitals and the anus.
Chant the sound LAM.

Open the Sacral Chakra

Put your hands in your lap, palms up, on top of each other. Left hand underneath, its palm touching the back of the fingers of the right hand. The tips of the thumbs touch gently.
Concentrate on the Sacral chakra at the sacral bone (on the lower back).
Chant the sound VAM.

 Open the Navel Chakra

Put your hands before your stomach, slightly below your solar plexus. Let the fingers join at the tops, all pointing away from you. Cross the thumbs. It is important to straighten the fingers.
Concentrate on the Navel chakra located on the spine, a bit above the level of the navel.
Chant the sound RAM.

 Open the Heart Chakra

Sit cross-legged. Let the tips of your index finger and thumb touch. Put your left hand on your left knee and your right hand in front of the lower part of your breast bone (so a bit above the solar plexus).
Concentrate on the Heart chakra at the spine, level with the heart.
Chant the sound YAM (as this mudra is particularly powerful, this may not be needed).

 Open the Throat Chakra

Cross your fingers on the inside of your hands, without the thumbs. Let the thumbs touch at the tops, and pull them slightly up.
Concentrate on the Throat chakra at the base of the throat.
Chant the sound HAM.

 Open the Third Eye Chakra

Put your hands before the lower part of your breast. The middle fingers are straight and touch at the tops, pointing forward. The other fingers are bended and touch at the upper two phalanges. The thumbs point towards you and touch at the tops.
Concentrate on the Third Eye chakra slightly above the point between the eyebrows.
Chant the sound OM or AUM.

 Open the Crown Chakra

Put your hands before your stomach. Let the ring fingers point up, touching at their tops. Cross the rest of your fingers, with the left thumb underneath the right.
Concentrate on the Crown chakra at the top of your head.
Chant the sound NG.

Warning: don't open the Crown chakra while you don't have a strong Root chakra.