I agree with Inkdux on Germany needing to wipe out most of the Allied navy. This forces Britain, with national production of 25, to focus on building expensive navy units. This also will put the US in a position where they must also beef up their navy to clear out what remains of the German navy. This takes the focus of the western allies off of amphibious assaults and more on building destroyers ($12 each) to destroy the German subs and to defend transports. This allows Germany to weaken its forces in France and put them against Russia on the other front. Germany will eventually have to contend with an amphibious assault on France but will have ample time to shift units into place for defense. Leaving the Allied navy alone and only going after convoys is a doomed strategy. Britain and the US will be able to knock your subs out of most of these convoys before they receive their money at the end of their respective rounds, which means the affect on their IPCs is minimal to nothing and you just got most if not all of your subs sunk. Once this is done, expect amphibious landings from the US and Britain to follow immediately, which takes Germany from being on offense to being on defense and is normally the beginning of the end.
As far as the eastern front is concerned, purchase a transport and put it in the Danish Sea and artillery to be placed either in Germany or Poland with the $12 you start with. Attack Leningrad with 2 infantry + 2 artillery transported over from Germany + 1 fighter. Attack Baltic States (only 3 russian infantry), East Poland (only 4 russian infantry) & Bessarabia (only 1 infantry + 1 armor defending) as well. Reinforce Rumania on your non-combat phase to prevent units from Ukraine from taking it in a counter-attack. If Leningrad is stacked with infantry, send the 2 infantry + 2 artillery with the transports to attack Baltic States. The extra transport gives you more flexibility in attacking on the opening round and can also help you beyond the 1st round as long as they stay alive. Britain has to choose on its turn whether to use its 2 fighters and bomber to attack your 2 transports or assist its remaining destroyers in Davis Strait and/or Strait of Gibraltar in attacking your subs (this is assuming you have concentrated all of your sub efforts in the first round to destroying the British fleet in the North Sea, English Channel & Celtic Sea). More often than not, they will choose to go after your subs to stop you from attacking their convoys as well as future naval units that they purchase. Your 1st objective should remain taking out Leningrad. If you don’t, this will allow the Russians to continually stack infantry there for use as cannonfodder in counterattacks or just to reinforce other provinces in the area, which will slow down your offensive tremendously. Even if you take Leningrad and they take it back in the next round, they still can’t build units there and you will most likely be able to take it back on your next turn. With Leningrad gone, Russia is forced to produce infantry in Moscow or Stalingrad. The combination of the US & UK being delayed due to their navies being destroyed coupled with Germany being able to transfer infantry and artillery to the front very quickly with the transports will put you in an excellent position to take Russia out.
As for the Middle East, in the first round take 1 artillery + 1 infantry on the transport and amphibious assault libya and move your battleship and destroyer in for offshore support while attacking from Tunisia as well. If Britain attacks your battleship, destroyer & transport on their turn with their fighter, destroyer and transport, you have the edge in defense numbers (4, 3, 1 vs. 3, 3 & NA) + the fact that it takes 2 shots to take down a battleship, so in essence its 4 vs. 2 and you should win this battle almost every time. On the 2nd turn, if Britain does not attack, pick up an artillery or infantry from Greece as well as the infantry from Crete for an amphibious assault on Egypt. You will have to use your battleship and destroyer to take out the British destroyer and transport, but again you have the attack numbers advantage (4, 3 vs. 3, 1) as well as the 2-shot battleship, so it is 3 vs. 2. Bring all of your forces from Libya to bear on Egypt along with the aforementioned amphibious assault. In subsequent rounds use your remaining forces to push through the middle east to Russia. This middle-east strategy does not seem very popular on the forum, but moving the German battleship, destroyer and transport to the Atlantic and leaving the British with all of their naval and ground units in tact will allow them to take Germany out of Africa rather quickly and force Germany to leave defensive forces in Greece and Southern Italy that could be used on the Russian front. Taking Britain out of Africa has 3 benefits: it allows Germany to leave places like Greece and Southern Italy completely undefended and gives them the ability to bring those units to bear on Russia, it takes money directly out of the allies pockets and is much more long term than attacking the convoys and it will eventually expose the Russian southern flank and force Russia to shift valuable units to Caucasus for defense. Using these 3 strategies in combination will put you in the drivers seat and will keep the allies on the defensive for a few rounds.