Having the concepts of manual machining before venturing into the CNC programming world will benefit you greatly. One is much more successful at CNC programming if they can mentally envision how a part will actually be cut inside the CNC machine. As far as which techniques are best to use when programming an individual part, there is no rule book. There is not a series of yes/no questions to be answered to determine how to do it. It is a matter of experience in machining and practice with the software, trying different selections until the results desired are obtained.