This is the first part of the process I go through in designing a new circuit, since I am not a professional in this field, I cannot make the claim that this is the way to design circuits, so I can only share my methodology of designing circuits at a hobby level.
The method I came up with is in steps.
1) Draw up the circuit in a simple conceptual form, mainly block diagrams, to see if the concept will work.
2) Draw up the circuit in schematic form.
3) secure as much information on the characterstics of a component, then calculate key voltages in different parts of the circuit, as refrence votages to bench mark off of.
4) breadboard (protobuild) the circuit one stage at a time, and test the circuit to make sure the actual voltage measurements are within the range of the benchmark voltages that were calculated in the previous step.
5) as the circuit build continues begin coupling stages, keep calculating and checking voltages in key areas, as well as testing the circuit performance after each stage is added in.
6) when problems arise, begin to solve it by removing stages sometimes one component at a time, until proper working, then start the process of analysing why the problem arisen.
that includes testing with new components to make sure components are working right, looking over the circuit topology, reworking the circuit build until proper performance at theat stage.
7) Then get a good full understanding of why it was not working and what was needed to fix the problem.
8) continue the whole process from step one all the way through for the rest of the build.
9) when the circuit is working properly, then test it by raising and lowering the voltage supply, to determine the best voltage value it will work at, and if it needs more rework for a chosen supply voltage, or if the voltage i not acceptable, then a whole new designed circuit may be in order.
These steps just come inherently, as I build along, sometimes there not always followed in that sequence,but just a little methid I use working this at a hobby level.
Part 2 gets into more intense detail of why the circuit later gave some very erratic outputs under certain input conditions, and how again I systematicallly worked through it to determine the cause and how to apply the fix, for it to finally be a properly working circuit as designed.
This is not a proffesional tutorial, but just for the entertainment of watching a hobbyist way of playing around with circuit design.