Well you DEFINITELY want to make sure you socialize him with plenty of different people and places. You want to socialize him because it helps him learn not to be afraid and act aggressively in new situations, as well as teaches him what to look for as to who is right and who is bad news. Don't want that a loaded gun going off at the wrong times (so to speak).
As for training, there's tons of videos on youtube. Clicker training is effective and many dogs take to it quickly. Positive training as well. Clicker training is simply the sound of a click taking place of a "yes" when the dog does the correct action based on the desired command. A click marks faster than a verbal acknowledgement which works better for some people. It really just depends on you.
Check youtube for videos by Tab289. He has a GSD that is clicker trained and he's a very good trainer. You can learn a great deal from his videos as he gives great explanations and demonstrations.
Shasta GSD 5/5/10 CGC, ITD, TC
"Dax" Thor z vom Weberhaus BCAT CAX2 CGCA ETD HCT NCO-1 PKD-T RATI RATN RA TC TKA 3/18/2013
"Hades" Guilty vom Blutfeuer 10/26/2018
Zena GSD 6/1/03-2/16/2016
Riley GSD/BC 1/10/05-2/1/2013