Rama has chanted this continuously for 9 times before encountering Ravana and attained success.
Aditya = the Sun God; Hridayam = that which is especially nourishing and healing for the heart.
It should be chanted in the day time. Morning after sunrise by facing the sun God. Do not chant after 12/30 pm. On sundays after chanting this sloka offer curd as naivedya to Sun God.
Sankalpa should be done and start the Aditya Hrudya Stotra -- pronounce each akshara clearly.
Sage Agasthya Muni gave this powerful Mantra to Sri Rama when Rama was perplexed, while fighting with Ravana. After chanting this Hymn nine times Sri Rama defeated Ravana.
The Aditya Hridayam, is a hymn in glorification of the Sun or Surya and was recited by the great sage Agastya to Lord Rama on the battlefield before fighting with Ravana. This historic hymn starts at the beginning of the Battle with Ravana, when Lord Rama is fatigued and getting ready to fight. The mystical hymn is directed to the Sun God, the illustrious lord of all victories.
Surya - the Sun God
Trying to do justice to verses from the epic Ramayana – the first of all epics in the world – written over 5000 years ago, is impossible by anybody today. And for that matter, Sage Valmiki himself says that the prayer part is older than the epic itself. That must be obviously true, for, Sanskrit language existed in its poetic, prosaic and pristine form much before the penning of the epic. I have just attempted to give the limited version of my understanding of the Slokas (verses). Mistakes, if any, are all mine, and any praise for the work goes to blessings of Lord Ganesha, Lord Rama, the Sun God, and of course Sage Valmiki.
The Adityta-Hridyam Stotra is part of the Yuddha Kanda of Valmiki Ramayana (the chapter of war) and contains 31 slokas.