Theravada Buddhism has laid out a map of progress towards Enlightenment in the practice of insight Meditation. I won’t go into details here. I will only highlight the key points. Feel free to research it more on your own.
Your practice will take you through 4 cycles Theravada Buddhism calls Paths. The first Path will lead you to Stream Entry which is the first level of Enlightenment. The main characteristic is that for the first time you will see the illusion of reality. It won’t be permanent, but it will reoccur on its own accord. After a while you will start another Path which will lead you to become a Once Returner. The next Path will make of you an Anagami or None Returner. And finally the fourth and last Path will take you to Arahantship. What each step entails is in my opinion irrelevant at this point. I think you should only care about it once you get there.
Each Path will have you go through series of steps. I will only list the ones that I think are the most important milestones. They are the Arising and Passing Away, what’s commonly called the Dark Night and Fruition. If you want to get more granular and study all the steps, read up on Theravada Buddhism.
The Arising and Passing Away is very different for each individual. It usually happens in the middle of a meditation and it is often trippy in the sense that it involves a flourish of sensations (visions, sounds, lightshows, bliss and so on). After it, you will feel elated, extattic and happy.
The Dark Night is where reality catches up with you to ask for receipts. It’s pretty gloomy. You will doubt and worry you might be making it all up. Your motivation for the practice will drop. It will feel like a depression. You can only wait it out. Look at the bigger picture and keep working.
The Fruition is an event that will happen in your meditation on several consecutive occasions. It is hard to describe. You will feel a dip, as if you were falling. It will feel like reality just stopped and restarted. I recommend you study it, but it’s very confusing, so don’t stress it. Only take Fruition as a signal that you are nearing the end of a Path.
If you see one of these steps, you could be wrong, so only take a mental note (record it in your journal) and keep going. Once you see those three steps back to back, now you have enough evidence to assume you are near the end of a Path. Remember it is only an assumption. Look the demon of self-delusion in the eyes and keep practicing.