If you have not tried to meditate...

First you should just start with a simple repeating of Om (aum) or Om Nama Shivaya or Om Shri Ram Jai Ram, Jai Jai Rama.

The secret Mantra (Excerpt from Story of Vishwamitra)

Vishwamitra Speaks:

The last barrier was, jealousy. Now you have conquered that enemy also. Hail Brahmarshi Vishwamitra! As Vasishta touched the brow center of Vishwamitra, his third eye opened and he saw the seven rhythms with which the cosmos was created. The sacred Gayatri Mantra with its seven vyahritis or rhythms was revealed to him at that time, thus:

OM BHUH, OM BHUVAHA, OM SVAHA, OM MAHA, OM JANAHA, OM TAPAHA, OM SATYAM,

OM TAT SAVITUR VARENYAM, BHARGO DEVASYA DEEMAHI, DHIYO YONAHA PRACHODAYAT, OM APO JYOTI, RASOMRITAM

BRAHMA BHUR BHUVAHA SVAROM

Translation:

May we meditate on the effulgent light of Him who is worshipful and who has created all the worlds. May He illumine our intellect. Brahmarshi Vishwamitra experienced cosmic consciousness. He was established in that highest consciousness forever and became immortal! Man may fall many times in his (or her) spiritual journey, but let him never give up until he attains the Supreme.

Daily practice is good...

It will be good practice to repeat the mantra every day, at least 12 times. It will be better to go for 40 days without missing a day. It is best to repeat it 108 times a day with a mala (rosary) of tulasi wood or rudraksha. Try a 40 day sadhana, if you miss a day, just start at day one again. By the time you have completed the 40th day, the mantra will be deep in your consciousness.

Get the initiation of a Guru

It is a necessary step in our spiritual evolution to become opened up or unblocked by a guide or Guru. The universal light will contact you if you try to contact them. They are set up for this purpose. Do not try to find a Guru, just be ready and the right one will be available when you are ready.