In the second jhana we are experiencing joyful delight and bliss and this joy is effortlessly flowing through us and there is a distinct sense of mental “flow” and unification. The joy is a more stable mental object, and we can center on that experience, and bask in the effortless joy, let it saturate and soak you and sooth you. The joy satisfies some deep longing we have and makes us feel alive and vibrant. It feels deliciously pleasurable and we can bask in it and enjoy the intensity of the energy and aliveness. But there is a limit to how long we can hold this level of excitement. Eventually the mind prefers a more mellow, lower energy type of bliss. This satisfaction and coming to equanimity in regard to the factors of the jhana, is a continual cycle we want to watch and learn from, and it occurs in each jhana.
When we see that the mind is satisfied with joy, we can simply widen the attentional frame out a bit, and focus on the outbreaths or in the belly. We can use a belly focus, or whatever area of the body seems to mellow things out and move from a highly excited, intense joy, to a contented, satisfied peaceful happiness. This lower-energy state is much more soothing and sustainable. We simply try to notice the mind in the 2nd jhana and notice any subtle craving or aversion- these are what moves the mind through the jhanas at a certain level of refinement it is possible to see this.
The bliss of 3rd jhana is a permeating, deep physical comfort that a meditator would be glad to spend all day embraced in the delicious comfort of 3rd jhana. In fact, just writing this makes the state being to arise for me. The bliss is soothing and seems to be a more refined bliss than the energetic bliss of the 2nd jhana. There can still be vibratory sensations of energy but these take a soothing, blissful feel to them and can be quite subtle. The mind is relaxed and contented and there is a distinct sense of utter comfort and contentment.
Meditators sometimes have trouble staying in the 3rd jhana because of the way the attention is shaped. It is a state where the awareness is broadly distributed- we are focused on a mental experience and the physical pleasure and excited joy have died down, and there is pervasive mindfulness. The mind is contented and also very secure in its own metacognitive perspective. The mind is contented and blissful and aware. There is a transcendent, almost mystical sense that this state can take on when some formless aspects of the 5th jhana are incorporated. We can refer to advanced jhana practice for detailed discussion of this and other jhanic states. Eventually, after some time basking in the contented bliss of 3rd jhana, the meditator can come to a state of profound equanimity, which is the basis of 4th jhana and the higher immaterial jhanas.