Some people, myself included, like Shaila Catherine's books about jhāna: Focused & Fearless and Wisdom Wide & Deep. The former was written before she studied with Pa Auk Sayadaw, and the latter afterwards (he asked her to write it). They are full of instructions on entering and sustaining jhāna, and Wisdom Wide & Deep combines Abhidhamma, Visuddhimagga and Sutta approaches with lots of scholaraly references.
I also like the Ajahn Lee/Ajahn Fuang/Ajhan Geoff (Thannisaro) approach which is very different but, IMO, extremely compatible with the above. Then again, I also like pulling my mind in several directions, so just consider that another caveat lector.
IMO, there is not one way to enter jhāna. IMO, if you have to ask a teacher of friend if it's jhāna, it's probably not.
Metta-bhavana is personally one of my favorite ways to cultivate the jhāna factors.
"INQUISITORS": Maybe it's helpful to talk about cultivating the jhāna factors instead of entering jhāna?