To help people develop a jhana practice I am going to elucidate exactly what I did and formulate it into instructions here.
Jhana is a mental state where there are certain mental qualities present and certain mental qualities are absent. Skillful qualities are qualities of mind that lead to insight and cessation of dukkha, while unskillful qualities are sources of dukkha and hindrances to insight. As such, a general strategy is to maximize skillful qualities and minimize unskillful qualities.

The best way to approach jhana is to continually and persistently try to evoke positive qualities of mind. Trying is a very light touch here, it’s really just enjoying oneself in the now. This skill can be trained even outside of formal seated meditation. The key is to appreciate and enjoy pleasant experiences and learn to rest in the present moment with a pleasant experience and not cling. The not clinging is an important part. That comes about naturally with the right approach.

When sitting on the cushion, rest and relax and appreciate the burden of everything being dropped. You are able to rest in your practice and you’ve released a burden of unnecessary doing. Then, without looking to hard or forcing anything, just try to find an experience (easiest at first is a physical sensation) that is pleasant and peaceful.

For me the feeling of my butt sitting on the cushion has a pleasant tone to it, and it’s a subtle comfort but it is easy to rest there as the center of my awareness. I rest in that, and breath in the most pleasant, relaxing, soothing way possible. Slow deep breaths are good for some times, while other times a shallower breathing is better. Now, feel the pleasantness of the breath, and the pleasantness of your chosen focus area/spot, and just work them in together. You can focus on the pleasant spot mostly and notice how the breathing affects how everything feels. You want to enjoy whatever pleasure and comfort you feel, without judging it or trying to make it anything else. Do this for as long as it takes you to feel a noticeably pleasant tone to the breathing and your focus spot. It might not happen right away, but you try notice whatever pleasantness, even if it’s very subtle and that will condition the mind to have more such experiences of withdrawal from the hindrances and seclusion of the mind. This intention over time accumulates karma and conditions further experiences of withdrawal and seclusion. Over time, persisting with this practice will lead to increasingly deep and intense feelings of pleasure and comfort.

Your intention in mind is to drop unskillful qualities of mind and attachment to sensuality. This means that you are “secluding” the mind from the hindrances and worldly thoughts, for the moment. Each moment with this attitude of renunciation, is accumulating karma that will condition a future intention and make it more robust. And at first when you learn to focus on a pleasurable object, it will be subtle and therefore you need to stay alert to stay with it. This trains mindfulness and counteracts dullness. Over time, persisting with this practice will lead to increasingly deep and intense feelings of pleasure and comfort.

Avoid taking energetic sensations as your focus area, unless they are pleasurable. 1st jhana in its essence is pleasure, and if whatever energetic phenomena occurring in the body are intense and unpleasant, some remedial physical practices and purification of conduct are recommended, if applicable.
The pleasantness will eventually be a good, noticeable, sustainable object, and then at that point, you will notice that there seems to be a “crest” of the wave of how you experience the pleasure, where it is very similar to orgasm but pervasive throughout the body. There will be waves of the pleasure moving through you and it’s kind of like surfing, you tune into the wave and it exands into the whole body. The way you stay with that is to learn to notice when the sense of pleasure seems to expand to the whole body, see that happening, and learn to stay with the crescendo of that wave. The way that feels in the mind is both relaxing and striking attention, it is a very light directing of the mind toward the rapture, but also relaxing into it. It is a “sweet spot” of your mental posture, essentially, and staying with that maintains the first jhana. These two mental movements, the striking and the relaxing, are applied and sustained attention, two factors of the first jhana. The other factors are rapture and happiness. There is also a “direct thought and evaluation” mental factor- which is a meta level evaluation of what’s happening. You are aware that you are experiencing rapture and happiness, and you are paying attention to the state with discernment.