There are several means to this goal - through Mantra, through Diksha ( or transfer of Divine energy from Guru to disciple), Kriya Yog, Prannayam, Ras Vigyan (use of consecrated and Samskarised mercury) and even Ayurvedic herbs and potions.

Yet the best way is of Mantra Sadhana for it is the most safe and can be tried by anyone. When Kundalini is activated there is a tremendous gush of energy which can cause great harm if not properly channelised through the body. But the Mantra Sadhana process is a slow and steady method totally free of such risk. Moreover this is done under the guidance of an accomplished Guru who can fully control the Kundalini. In this Mantra process the six Chakras are activated one at a time and there are seven stages of this Sadhana.

Whatever the mode of activation a Guru is a must for during the process as the divine powers in the body come to life they attack the Sadhak's weaknesses like greed, jealousy, infatuation, anger, false ego and other negative traits. Sometimes the struggle between these positive (Kundalini) and negative energies can be so intense that a person may lose balance of mind or his evil traits may appear so magnified to him that he may take to wrong ways in life.

But if there is a Guru guiding each step of the process the negative energies can never come out on the top in this struggle. That is why the Guru also suggests Guru Mantra Sadhana for the power of Guru is so strong that it can annihilate all evil traits of the Sadhak.
It is also important to note that there are different Mantras for the activation of six Chakras. One may accomplish Sadhana pertaining to a Chakra and still not experience anything. Remember it is not a miracle we are working. It is a slow and steady process and sometimes it is after some months that suddenly one becomes aware of the activation of the concerned Chakra.
In truth after Sadhana the activation takes place when the Sadhak feels most purified and free of his negative traits. One should hence continue with Sadhana of other Chakras even if no immediate results seem forthcoming.
Sometimes two or three Chakras have been seen to be activated all of a sudden at one go.