From the first jhana there are basically three things a meditator can do: 1) get stuck there (I know someone who spent some twenty years cultivating the first jhana in daily practice, thinking that was insight practice); 2) progress to the second jhana; or 3) investigate the three characteristics of the first jhana and thus progress in insight. They can direct their attention to breaking the illusion of the solidity of that state into its component individual sensations so as to gain insight into their actual mode of momentary presentation.
