IJoin World Prayer before sleeping
You can do your own prayer. Here is only an example taken from Amma.

If you are still not convinced about the infinite power of Prayer, please read this scientific article before.

Amma says:

Please light this candle at 8:00 PM each night. Sit comfortably and close your eyes. Chanting, "Om lokaha samastaha sukino bhavantu", which means, "May all beings in all the worlds be peaceful and happy", continuously for 15 minutes. Remain with your eyes closed and imagine the light of the candle as the Divine Light. Imagine the light pervading the whole universe. As the light falls on each being, visualize that they attain peace and become filled with Divine Love. Picture the whole universe filled with peace and love. See yourself as part of that universe, bathed in Divine Love and Light. At the end of the prayer you can chant "Om shanti shanti shantihi" which means, "Peace, peace, peace."

Source: http://www.ammachi.org/main/light-n-peace.html

Here you have another three powerful prayers, and an article about the power of the collective prayer.