Abiding by the principle of each to his own re the games own in built choices in difficulty the other element I like to keep in mind is 'behaviour'.
I try and play the game in the most realistic way a real Kaleu might behave. To this end I read as much as I can get my hands on by way of diaries they might have kept and books that have been written on the subject. An excellent book I am busy making my way through now is "War Beneath the Sea", described as the standard work on the subject of submarine warfare.
Obviously I play 'dead is dead' (skipping the cyanide pill on my desk
) and my crew are 'real' to me so what decisions I take regarding attacking, surface re-loads etc are taken with their safety in mind plus the asset I have been trusted with - namely my boat. I avoid attacking destroyers at all costs if possible for example. And taking on planes is just not even something I would go out of my way to do.
A more recent example is my current patrol. I refuelled from a milk cow in June off the East coast of the States and was all keen to go back and patrol off New York and possibly do this many times as the milk cow was going to be stationed in the grid till Xmas. And in so doing rack up the tonnage hopefully. But Sailor Steve pointed out in my post on this that milk cows were primarily there to enable boats to get back home. So if that is how it was in reality - then its back to Lorient we go and not to 'game the game' so to speak.
But as I say, each to his own. Silent Hunter 3 is an enjoyable and enthralling game however you play it.