This is my second favorite book after The Ascent of Mount Carmel. However, it is challenging, so be patient with yourself as you go.
Many people get caught up in the concepts of levels, and ask themselves what level they have reached, and so forth. This misses the point.
There are many mansions, and in using this metaphor Teresa struggles to make her ineffable experience understandable. It is a work of mysticism. Some readers relate easily to her words while many more struggle and give up on reading more.
Two authors may help to break it down Carmelite concepts into “real world” terms. Each of them has a gift for making Carmelite prayer relevant for people not in holy orders. One is Father Marc Foley and the other is the spiritual director Anthony Lilles.
There is also a Teresian form of lectio divina which may easily be made to fit into daily life, which you may discover online.
As others have said, allow God to lead you into prayer. There is no wrong prayer, and Teresa writes of how God will lead the soul who honestly seeks him.
Labels and descriptions, as well as concepts of “advancement” in the spiritual life may have their place. Literary metaphors can be transcendent.
But what matters is letting God take the lead and surrendering to Divine Love. For me, this is the essence of Teresian prayer, and something each of us can do if we allow him to show us the way.