Cultivation In Real Life
You can consider living a long mortal life and it's experience as Qi Gathering (immortal way). You can consider the time when a mortal accept his dreams, ideas, thought out possible what if or alternatively different reality as past lives and the him of now is the base personality for the future and use those as experience and opportunities to understand things faster even if they have not experienced it as Foundation Establishment (immortal way). You can consider that the time a mortal anchor their current personality as the base and prepare for death and accept the different possibilities of death and avoid them or experience them to lay a barrier around themselves and nurture more experience and possibilities that are experienced in different ways and thought up of or even dreamed of as Core Formation (immortal way). The mortal can continue to live life or experience death but this also a tribulation as if the will is not strong their memories will be erased and not be able to experience birth from the moment of time intermingling of yin (female egg) and yang (male sperm) and use DNA of good quality and less bad like defects and establish a better mortal foundation and stronger soul or a conscious cluster of Qi or molecules. The mortal could continue to live longer and hope their soul is strong enough to hold their body together and maybe even slow or stop the aging of the body or with a strong foundation or soul can even reverse back to youth to a certain extent. Their may be chance where bad luck or tribulation start to happen and death may be present and if you get through it you can live longer and which can be considered as tribulation for the for the mortal and/or to advance or known as Nascent Soul (immortal way). This the last I'm going to give for now the mortal will have their soul strength increase and compress and experience quantitative and qualitative change or the conscious Qi or molecules compress and improve and gather more molecules and increase density or strength to hold mortal body but their will come a time of tribulation where the soul start getting weak and/or tired and the body might start to aging again and they have to will themselves to continue live and experience another qualitative change to the soul or conscious Qi or molecules which can be called Divinity Soul, Enlightened Soul, Transcendent Mortal, or Tribulation Crossing (immortal way) There are was to make this faster by living in virtual reality and experience different possibilities and death possibilities without putting the mortal body at harm and experience many things and may strength the soul faster.
Immortality through Religion
Immortal Through Religion is another possibility. I will talk about Christianity since I'm more familiar with it. You can say that God or the True God is the best to become immortal through in this religion. Some think that he is the only god. He said he is the only True God not the only god. He said he made humans in his image and likeness, so that mean he gave us the ability to do things like him. He created us so that mean we can create life or things that are in our image and likeness, which to an extent means we are little gods. So that mean that either every or most souls you see are either a part of the True God ,he took part of himself to create our souls, or he awakened first from the collected conscious and help nurture and awaken other souls ahead of time. What this mean is that we become gods or god like but never a True God like him. Immortality of is seen as a trait for gods or god like beings, immortals as an example. Anyway to become immortal through this way is to abide by their teaching in each religion. You are trying to make your god acknowledge you and use their power to increase your lifespan, and as you rise in ranks of your religion your knowledge increase, and also your body will be strength. You may even be able to gain and/or change into a new form and/or race, Angels for some religions. This way also means that you have to open yourself or soul to them and allow them to enter and change you so you can become immortal through their power. There will be other immortals or gods that will find souls and/or make religion it give a chance to mortals. There many ways to become immortal but these are the two easiest ways that I have come up with that have a higher chance of reaching Immortality. The other ways are harder to execute or performed. The first example can be seen in the real world and data can be found that being active let you live longer so what if you work with that goal in mind instead of passively get it as a benefit. This mean instead of working to gain strength with the side benefit of longer lifespan, we should work for longer lifespan with the side benefit of strength. There are many people that can become immortal because of religion. As they gain more followers and/or mortals and make a connection, that allows some gods and/or immortals may gain the knowledge of that followers which will help them step closer to becoming omniscient. Let me know how this theory sound, and if I should go further into the theory.