I feel like you will need to know power amplifier design fairly quickly. The consensus is to read Cripps's book. You should have a basic understanding of RF concepts like S-parameters, P1dB, impedance matching, Smith chart, etc. This stuff is covered in Pozar's book.
But the gist of PA design is to design impedance matching networks to transistors to present an optimal impedance to the transistor. By doing so you can get desired Pout, PAE, gain, etc. You also gotta figure out how to do this while keeping the amplifier stable, not to overheat, etc.