The English Channel becomes increasingly perilous as the war progresses. Personally the only time I would go through there is on an August 1939 shakedown cruise or, if my second patrol starts early enough, on my way out to an Atlantic patrol grid provided I can get in one end and out the other before the war starts.
Due to the shallow water there it's a very bad place to get caught out by the Royal Navy - plus I expect that some of it is going to be mined after Sept 1939 and given how narrow it is to begin with, that can't be a good thing for any u-boat trying to make the passage.
And on a "performance" note I find the heavy traffic there usually slows my play down to what seems like a standstill, especially trying to get between Dover and Calais submerged. Just too many contacts constantly dropping me back to 1 TC. And it's not like I'm going to go after any of them, because I don't want the RN or the RAF getting wind of my presence and coming after me there.
That said, I always set a course for my assigned grid when I begin a patrol and once I'm there I patrol it for the "required" 24 hours. I've modded the renown awards for doing so back into my game, mostly to avoid the temptation of ignoring my orders completely.
I'll have a go at any targets of opportunity that pop up along the way, and if I get a contact report of something I might be able to intercept without going too far off course I'll take a chance on that as well - but for the most part, I'm taking the shortest route to my assigned grid while still staying just out of range of the RAF and in the "friendliest" water possible for as long as I can. Since I'm only up to Sept 1940, this is not very difficult.
Once I've done my 24 hours, it's a toss-up. If I'm having success in the area, I'll usually stay there, maybe working my way into an adjoining grid every few days. If I get radio messages or contact reports that can be used as a "legitimate" reason to head off for another area entirely, I may do that. When I get to the point where I need to transfer my external eels into the tubes, that can serve as a reason to head for a quieter spot in which to attempt it. If I'm having a really good luck and closer to a resupply ship than home, I may eventually head there to refuel and rearm instead of returning to base, after which (according to the game) I have no "orders" to do anything in particular, so I can set a course more or less for home but set up camp anywhere I please if I find good hunting along the way.
It really is very open-ended, since even if you're still getting the stock renown award for following your initial orders, it's not necessary to follow them in order to "win" because it's not that kind of game in the first place. The only real way to win is to still be alive when the war's over. Everybody has his/her own way of determining what exactly to do on patrol, with varying levels of attempted "realism" according to what makes it a more satisfying experience for each individual. You'll just have to find a way of your own that makes playing the best experience for you at any given moment. And for that, experience will probably be the best teacher.
