First, I make all the theorical calculations respect to the design, so that it can work very well at least since this point of view. After this, I simulate it by using a properly software in order to make sure it works very well and its performance is optimal or at least acceptable according to the design criterias that were used. Third, I build the circuit in a protoboard, I make some tests and measures, compare practical and theorical results to see whether or not it is working well, then I make some fixes in order to improve its performance and correct the failures (if it has). Finally, when it is working well then I design the PCB circuit, build it, and make the final tests