Singing of Arati

Arati should be sung with bhav (spiritual emotion). Pronunciation of words correctly and singing arati after understanding its meaning prove to be helpful in singing arati with bhav

Why should a prayer be done for expressing gratitude?

Prayer is actually a synonym for surrender. This act of surrender is completed only after the expression of gratitude. Gratitude is a means of offering the doership of an act to God / the Guru; hence it helps in reducing the ego.