[The one best book that I think contains the basic essence of the Oral Law is the Avi Ezri of Rav Shach. The best of Metaphysics I think is Plato, Aristotle, Kant, Hegel, and the Guide for the Perplexed, even though the Rambam was referring specifically to Aristotle. ] [If you have finished the Avi Ezri then I recommend the basic books of the disciples of Rav Chaim Soloveitchik, Baruch Ber, and Shimon Skopf.]
There are a few ideas I had about Physics which mainly are base on the statement in the Talmud לעולם לגרוס ואחר כך להבין One should just say the words in order and after that understand. But along with that I found a few more ideas like review of the same material forty day in a row helpful. That is to read about a hundred page or so and then the next forty day to review the material forwards and backward. That is let's say you have got up to chapter 10, then to go back over chapter 10, then 9, then 8 etc.
But you must not think too hard about what you learn. The
source of authority must be dark, impenetrable and uncriticisable. Learning Physics is like learning Torah. The inner essence must be beyond human understanding and only by grace does one come to grasp.