Truthfully speaking, no one clearly knows; however, we have a few good hints about the nature of the practice he might have taught from some of the Buddhist scriptures. From the above scripture, it is clear Buddha felt that unless one was using a correct method, one could not expect to gain Nirvana—the fully awakened state of absolute freedom and enlightenment.
Buddha also spoke of two qualities that he thought were fundamental to the fully-awakened state: Tranquility and Insight.
Two things will lead you to supreme understanding. What are those two?
Tranquility and Insight.
If you develop tranquility, what benefit can you expect? Your mind will develop.
The benefit of a developed mind is that you are no longer a slave to your impulses.
If you develop insight, what benefit will it bring? You will find wisdom.
And the point of developing wisdom is that it brings you freedom from the blindness of ignorance.
A mind held bound by unconsidered impulse and ignorance can never develop true understanding. But by way of tranquility and insight the mind will find freedom.~ Anguttara Nikaya
It is interesting that the two most popular forms of Buddhist meditation that are taught today are called Samatha and Vipassana.
Samatha meditation is based on the intention and persistent effort on the part of the meditator to concentrate the mind on some specific object of meditation: the goal being to develop the ability of the mind to concentrate because when the mind is in a highly concentrated state, it is known to be tranquil and such a mind, it is thought, would make deep insight possible.
Since Buddha explained that only the right method would bring the fruit, it would be valuable to explore whether Samatha meditation, as it’s understood and practiced today, is the right method to bring tranquility to the mind. The term Samatha actually means calmness or tranquility: an integrated state where the mind is not in any way excited or active. It is directly related to the term Samadhi, the state in which the mind is completely settled and unwavering and is effortlessly held in a fully concentrated state.http://www.elephantjournal.com/2011/07/the-buddhas-meditation-dr-evan-finkelstein/