the most conventional way to win a domination victory is to get an advanced tech like Feudalism or Combustion, and then strike before the enemy more advanced defenders like riflemen or modern infantry.
But, the Germans are one of the few civs that do not need to be in the tech lead to win a comfortable domination victory. Their elite armies upgrade, so it's usually wise to delay iron working, build a barracks, and make a lot of warriors that will upgrade when you get iron working, feudalism, and combustion. Their medieval bonus, +1 production from forests makes it easy to get warriors out really quickly, espeically if you have 3 or more forests by your city. Note that you do not want to get your beaker count above 30, as this will usually backfill iron working.
Those elite armies hit really hard. Getting march, blitz, and infiltration is usually the best setup for your armies. You can get an army of 3 elite units, or you can build 2 more warriors/legions for 10 hammers, and then form an army with one elite warrior and then they will upgrade as you advance in tech.
Get feudalism and then Relgion, switch to fundamentalism, and you have knights that can attack at 27-36 or more, depending on upgrades and bonuses.
But, Game of the Week means each AI cap will have a Great Leader, a Barracks, Iron Working and Bronze Working to start the game. Usually you want to try and kill them before they get an archer army, because those archer armies have 27 defense in Deity GOTW. If you are going to play a long game, you'll either need a lot of elite knights quickly (with practice, you should be able to make about 5-10 elite knight armies by 0AD from 5-7 cities, only teching to feudalism).
GOTW on Deity isn't an easy win by any strech. Using spies to steal their Great Leaders helps if you get locked into a long game.
I usually don't expand that much with the Germans, I try to be efficent in tech and production, trying to get 5-7 cities, and then teching bronze, alphabet, writing, code of laws, iron working, monarchy and feudalism. That's if you want to strike quick. This works really well for online play. If you want a more well rounded game, you should target navigation after code of laws and try to get to the islands to help increase your tech.
They are not the best techers, but it's easy to stay alive with them because of their military bonuses, as well as their production bonus. You should always be looking for how the extra production can help you win, whether it be building more libraries, settlers, units, wonders, temples, or whatever you can do to convert that advantage into a win.