- Traveling at high seas can be rather boring, and it's tempting to crank up the time compressor up to max. Don't. While there are certain speeds recommended, the extreme speeds tend to weird the spawning and such out. You'll be unable to react to threats or targets appropriately. The game simply stops the high speed and the enemy destroyer comes out of the fog in mere seconds. End game. When in enemy waters with intense traffic it is especially likely.
- Being in a submarine does not mean you have to stay submerged all the time, keep surfaced unless there are threats or targets near by. You'll go much faster and be much more alert for targets. At the same time you can submerge occasionally to ping the hydrophone and figure if there are ships nearby. This is very useful until later in the war when you get a radio.
- Do not try to be a hero and take on military ships. While they are admittedly impressive kills they are actually rather low in tonnage, and they will chew your sub up and spit it back out in a heartbeat.
- Don't try to Rambo it. There might be a convoy of a hundred large merchants sitting helpless, but if you see even one destroyer you pop off your front torpedoes at the most tempting targets and then hightail it out of there.
- If you do have a Destroyer on your tail play it cool, dive deep and go slow. Turn on silent rigging and try not to make any sounds. Hopefully the Destroyer will drop some depth charges close, but not on you, decide that you aren't there and continue on elsewhere. Even a single depth charge can be fatal, as they weaken your structural integrity which can make deeper waters deadly to you.
- Planes. Especially a problem if you're heading around the Isles, when you spot a plane it's better to just submerge and let them past. Even if you have a flak gun, planes are hard to hit and can do major damage to you with just one hit. And as time passes they only get more deadly.
- Get all your fun times out of the way at the beginning of the game, because death is inevitable. You are a German U-Boat, no matter how good a captain you are there's no way for you to significantly alter the outcome of the war. As the years go by you'll find that your enemies because more advanced and better equipped, and while you'll get your hands on some rather nasty u-boats yourself..the enemy is always more numerous and becomes increasingly more competent and able to deal with you no matter how well you hide.
- Most of the people who play the game swear by turning all the realism options on and manually plotting their torpedo courses and such. I recommend you take a look at them, see what you think is cool and enable those. Don't be afraid to let the computer handle some stuff for you, the game has a rather steep learning curve and can be rather based on luck sometimes. Your first few games will likely be spent fighting the menus and controls until you run aground and die. You will probably also be torn apart by trying to find at least something hostile to sink in the open sea. Again, use the hydrophones, check radio messages, stay alert.
- Rather predictably the English Channel is crawling with mines and planes and is a veritable death-trap. Try to avoid it by going around the top of Scotland unless you have orders stating otherwise.
- Your sub is a fragile egg. Do not be afraid to let your prey go if you suspect that things might not go well, there will be plenty of chances to blow up merchants later.
- Try not to save mid-patrol, it tends to cause bugs and mess everything up. When you have things to do, you may as an exception. If do save in sea, your priority upon loading the save should be to reach the shore to properly save game progress. If you save mid-patrol, always make a few saves to reduce your chances of glitches upon loading. The best way to save progress. The easiest way to do itl to exit a mission with the back to base option when hitting escape. This is available in open sea with no enemies nearby. Or you can sail manually sail to for maximum realism and roleplay. You may anchor at whatever base you like and save there.

http://www.beforeiplay.com/index.php?title=Silent_Hunter_3 Original Source

And something from myself.
Do not ever, ever install mods that you are absolutely sure are compatible with each other. This concerns standard installation procedure with JSGME and simply installing rough files in the game and replacing them. It may make your game crash or act oddly (examples: no ships showing up, glitches, bugs, crew dying randomly).
So, always make sure to make a reserve copy of your game directory just in case something happens. Best to be very careful with supermods like GWX and other ones.