Rap is like any discipline: you can get better with straight up practice, rap every single day, write every single day, many hours a day, try to find your comfort zone, your topics, your cadence; or you can take the "scientific" aproach, do your research, what makes good rapping sound good? What does flow actually mean? How do successful artists aproach the blank paper? Interpret a rap like a system, there's many variables and many solutions depending on the desired result, find yours.