All for SOPs but also reminded of Trenchards remarks that rules are for the obedience of fools and the guidance of wise men (and women now I presume!) - by the way I am not ex military either!
It can be confusing for new FOs in particular when instructor pilots give (well meaning) advice which might SEEM to contradict the SOPs. Some matters do, I feel, come under the umbrella of Airmanship although they may not be "technically" in the SOPS. Checking the volts etc before putting a genny on line may not be required from a systems point of view but I seem to recall that on the B737 it was a good idea to check the volts etc before putting ground power on line in case the friendly ground crew chappie had selected the wrong parameters on his all singing dancing GPU!! Maybe this is where this habit has come from.
My advice is to have an open mind and take the bits you like from your experienced training captains since its based on a lot of hard experience! Get into the books and learn about the systems and see whether they are right. If they are worth their salt they will only be too glad to discuss your findings since this is how we all learn. That said SOPs are precisely that and should be adhered to but remember that Lord Nelson disobeyed orders to win a decisive battle but remember that if anything goes wrong its on your own head if you have not followed the SOPS!