Griffin
Seeing that Frees offers some interesting systematic strategies for developing insight into the 3C. For example, in StF anatta practice, you choose an aggregate and actively sustain a view of it as "not me, not mine". You are then encouraged to try doing the same with a different object, until you work through all the aggregates.
A relevant quote from StF, for context:
You have probably had the experience of an insight arising spontaneously as you were being mindfully present with something. You ‘have’ or ‘get’ an insight. There is an ‘aha!’ moment (...) This mode of insight practice is in contrast to another mode in which we can also work at times, where insight itself is more a starting point, a cause, more itself the method. In this second mode of insight practice we more deliberately attempt to sustain a ‘way of looking’ at experience – a view of, or relationship with, experience – that is already informed by a certain insight or other. Here, rather than ‘getting’ (or hoping to ‘get’) an insight, we are using an insight. Here, rather than ‘getting’ (or hoping to ‘get’) an insight, we are using an insight. This does not mean merely to ‘think something insightful’, for instance that “all things are impermanent” – thinking may or may not be involved – but actually to shift into a mode where we are looking through the lens of a particular insight (looking deliberately for and at the l impermanence and change in everything, for example). (...) Being repeated, the insight is more likely to be gradually absorbed and to become rooted in the heart’s understanding in ways that can make a long-term difference.
