You Know who i am to read title, I am very freshman in Analog circuit.
So, please give me your generosity...

Question:
Most of the analog circuit needs some bias voltage.

Is there some rule on bias voltage selection?
Simply should I do simulation and find the condition or size of transistor for saturation mode by trial and error?
Or should I manually calculate all transistor's DC level for saturation and start to satisfy calculation result ?

And is there any best way to select proper transistor size?
If i choose the bias condition, I can make the circuit in various size and scheme. Then What does make me select the best size of transistor?