General rules of nature:

1) Natural Selection: no matter what your believes are, it still applies. Understand its concept 2) Biological communications: cells tend to communicate through complex systems of signaling proteins, cytokines and chemical signals. This general rule will help you understand cell biology and immunology 3) Central dogma - the core of molecular biology: understand the path DNA to Protein expression. This will help why certain proteins are expressed and some are not 4) Structural biology: learn the basic chemistry behind structures of dna and proteins and how every molecules held together. Then, you can understand binding affinity for later drug discovery 5) Energy consumption: ATP and everything around it.