In Dzogchen it is simply resting undistracted in natural state.

It is free from all mental constructions, while remaining fully relaxed, without any
distraction or grasping.

How we know when it is rigpa and when it is not? If you are in an unaltered state,
it is rigpa. If not contriving or manipulating the mind in any way, but simply
resting in an unaltered state of pure and pristine awareness.

When one past thought has ceased and a future thought has not yet risen, in that
gap, in between, there is a consciousness of the present moment; fresh, virgin,
unaltered naked awareness. Another thought suddenly arises. This is if recognized,
the self-radiance of that rigpa awareness.

In cutting through, the practitioner rests in attention and lets that attention cut
through the confusion of thought and projection to the natural purity of timeless
awareness itself.

As soon as a thought arises, rest (and relax the posture). Then look again.
Work with this alternation, the looking and the resting.