Germany is, in my opinion, probably the most interesting country to play. Unlike Italy, Turkey, and England, it has a potential rapid growth path. And only Russia matches Germany in terms of the number and diversity of possible opening strategies. The key to playing Germany is to understand her strengths and weaknesses.
Germany's key strength is a central position which allows for rapid expansion (there are 10 SCs within two moves of Germany's home centers). Another strength is an easily defensible land border in the west and the fact that you can pretty much count on Austria not attacking early across the Barren Zone (Trl, Boh, Sil, Pru).
Germany's central vulnerability is almost always a lack of fleet strength. This plays itself out in two ways. First in the short run, a lot of German players get themselves in trouble by focussing on Den, Bel, and Hol. Since England will almost always hold Nth, a single English fleet can tie up three German units trying to hold those centers. Of course, if you don't tie up those units, you risk being stabbed by England. So rapid expansion on the North Sea periphery is something to be avoided. Better to buy English friendship by supporting him into Bel than demanding it for yourself.
Second, over time, Germany oftens faces a seaborne threat from either France or England -- whichever has won the naval battle of the Channel -- and a seaborne attack will eventually erode virtually any land-based German position, no matter how large. I think that an E/G alliance is usually going to spell trouble for Germany, especially if England is played by any sort of competent and/or ruthless player (I tend to equal competent with ruthless in a dip player). Simply put, with superior fleet strength England can wage war on Germany with impunity. The solution? Kill England early if possible. But if you can't bring that off, the next best choice is to develop your own fleet strength, or at least threaten to build your own fleet strength unless England agrees to send his fleets off into the Med. F/G is less dangerous because France will often get wrapped up in the Med, and in any case France can build F Mar which, unlike English builds, does not have to move along the German flank to get into combat.
This forms the background for my assessment of German openings:
The Western Triple. Do not join one. In fact, neither France nor Germany have much to gain from a Western Triple. England gets to Stp before Germany gets to Mos, and before France starts taking Italian centers en masse. So, by 1903 England will have a choice of stabbing either France or Germany. Germany usually is the one to get it. The only time a Western Triple makes any sense is when there is a strong R/T alliance. Even then, you'll likely get killed, but since R/T can sweep the board in any case, you might as well try what you can.
E/G. A decent choice when dealing with a difficult France. Buy English friendship with Bel. Hope that Italy can be made to move to Pie. France is a tough nut even with a concerted E/G. In the long run you probably will need to get rid of England though, so cultivate Russia early. This strategy is risky. If you can't dominate the west before the east gets settled it is easy to get caught with your pants down. And encouraging Russia into Scandinavia can sometimes lead to being attacked by Russian fleets from the north and armies from the east.
F/G. This seems to me to make the most sense. The key, I think, is to make sure France understands the tradeoff of position for centers. I'd be willing to give France a disproportionate percentage of the spoils in exchange for a very limited French fleet presence up north. But if France insists upon keeping fleets in northern waters, then you can't let her also have the centers.
I don't like the other openings -- north into Scandinavia, east into Russia, or southeast into Austria. You just leave yourself too open to attacks from the rear. Some people suggest sending a single unit off to Sil, Boh, or Trl as a bargaining chip. I think that's one of those ideas that sounds great in a strategy article but in practice pisses people off for no good purpose while blunt your offensive strength in your main theater of action. Now, that does not mean you can't threaten or hint at different openings in order to gain diplomatic leverage, but I think Germany is just as well off to play the opening straight.
In short, I think Germany has a lot of potential, but with only three countries in the west, it is imperative to settle the E/F/G triangle early and cleanly. And it is crucial that this settlement, whatever it may be, does not leave you open to an easy seaborne stab.
What you do after the opening depends on what has happened elsewhere on the board. F/G can go a long way. A/G is an interesting alliance and works as long as you can keep a seaborne power on your side until the endgame. G/T works well too. G/R will often run into problems as soon as dividing up Austria gets discussed, although as long as there remains a strong southern third party, Russia can often help guard your flank as you finish in the west.
Some will argue that my focus on seaborne threats is misplaced, that the danger for Germany comes from its central position generally and that the key is to get to the edge of the board. I think that is valuable advice if possible, but it is the potential inability to strike back against sea power that keeps me up at night. I mean, let's say you take out Russia. Start off E/G, kill France, then as England goes into the Med, you work with Austria in the east. If all goes well, you add Stp, War, and Mos to Hol, Den, Swe and your home centers. If England then attacks you will lose Hol, Den, Stp, and anything in Scandinavia. Your line of defense becomes Kie. Easy pickin' for your former Austrian ally, eh?
Let me add one more point. I think that as a central power it is usually wise to kill off as many other players as possible. "Well, of course," you are all saying, "you always need to kill players to win." Yes, that is true, but I think it.is especially important as a central power. The edge powers can often benefit from keeping lots of minor powers around and squabbling. It keeps things loose enough for them to seize a dominant position and carries few risks. For a central power, it means more countries who might decide to go for your more attainable centers.
So my advice: settle the west, guard against seaborne attack, and kill as many players as possible as quickly as possible. In a fast, ruthless, blitzkrieg game Germany has the advantage.