Read a passage from the Bible, Bhagavad Gita, A Course in Miracles or any scripture or spiritual book, a prayer, a shloka or a mantra. Learn it and understand its meaning. Repeat it over and over again like a mantra while contemplating its meaning. The benefits cannot be described but have to be experienced.
Two verses I think are apt:
The Gayatri Mantra
Aum Bhur Bhuva Svah
Tat Savitur Varenyam
Bhargo Devasya Dhimahi
Dhiyo Yo Naha Prachodayat
On the absolute reality and its planes,
On that finest spiritual light,
We meditate, as remover of obstacles
That it may inspire and enlighten us.
Listen to an audio version of the Gayatri Mantra being chanted 108 times here
2. Sri Aurobindo Gayatri
Let us meditate on the most auspicious(best) form of Savitri, on the Light of the Supreme which shall illumine us with the Truth.
Listen to audio version of Sri Aurobindo Gayatri being chanted 108 times here