From the Book Beyond Mindfulness in Plain English by Bhante Henepola Gunaratana.
The Second Arupa:
The Base of Boundless Consciousness
To attain the second arupa, you must achieve full mastery over the first and then see its defects. It is still close to the material jhanas and it is less peaceful than the attainments above it. You reflect on these defects until they are real to you. Then the mind naturally develops indifference toward the first arupa and you turn your attention toward the second.
By completely surmounting the base consisting of boundless space,
aware of “unbounded consciousness” he enters and dwells in the base consisting of boundless consciousness.
You focus upon the consciousness that is aware of that boundless space. This consciousness is also boundless and even more refined. You advert to it as “boundless consciousness” or “simply as awareness, awareness.” Your object is awareness but you always keep that boundless, infinite nature in mind.
These are normal conscious thoughts and you turn to them again and again. You repeat to yourself over and over “awareness, awareness.” The hindrances are restrained and the mind enters access concentration. You continue to cultivate the counterpart sign that results. There follows a moment of complete engagement in the “base of boundless consciousness.”