Raja-yoga is the process to attain the Divine by ignighting the flame of knowledge of self within. And for so, the seeker should develop strong willpower through relentless practices of concentration and meditation on self, through Pranayam and Asana and an uncompromising austerity and self-control, i.e will.
According to Raja-yoga, in its guidelines for reaching the goal of self-realization - focusing the mind on the same object for twelve seconds achives one unit of concentration; twelve such units of concentration (2-min 24-sec) make one unit of meditation; twelve such successive units of meditation (28-min 48-sec) make one unit of lower samadhi; twelve such successive units of lower samadhi (5-hrs 48-min 36-sec) leads to asamprajnata samadhi (the highest samadhi), the final spiritual & goal.
Success in raja-yoga depends on the moral fitness and earnestness of the seeker.
For more details one can go through the PATANJALI , the founder of raja-yoga.