Xibei San Ma
Playing as Sweden is actually rather easy, all you have to is play out the major powers against each other.
First order of business is to get another research team, so build 6 IC each in 3 provinces (it doesn't matter which provinces you build them in since you won't be fighting in Sweden. Move the slider to more free market to get better build bonuses. You could also move the sliders towards Authoritarian if you want to invade Norway later. Just keep building IC and researching industry, infantry & upgrade your troops in peacetime but then again, it doesn't matter much since you won't be using Swedish forces to win the war. Kill time by improving relations with Germany.
Join the first winter war to get more interventionism and if possible try to take control over the Finnish forces. Don't bother actually trying to win the war by sending your troops into Finland. The SU is just too powerful and you won't gain anything by invading SU from Finland. Instead just let the war drag on and make sure that FIN is weak but not weak enough to be annexed (yet). When the peace-events comes, accept them. By now, FIN is rather weak and should probably have lost a lot of divisions. And now you are back to peace.
The Waiting Game
Germany will probably run over SU at first so you can just relax for a while and also all of your factories should be done about this time so start producing some Marines and Mountaineers. After a couple of months you should be ready to join the Axis so take military control over Germany and Finland. Move Guderians 9 Panzer to Luleå and at the same time make sure that Finland is annex by SU. At the same time make sure that you kill as many Russian divisions as possible with German forces, since it's not your troops or your land you can have fun with all kinds of strategies. When the SU have annexed Finland and most Russian forces are dead, withdraw all German forces from SU and put them on hold in Poland. Now is the time to strike out from Sweden with German panzer. In a matter of months you should have control over all the Baltic's. From there you just have to push forward and annex SU from Swedish territory.
And voilà, a new Swedish empire. From there you can pretty much do whatever you want. Maybe strike into china? Maybe take Norway? Maybe attack Turkey and push forward into Africa?
This was tested in 1.02
Sweden has during her lifetime avoided war and the Swedish people are rather avoiding to interfere in any hostile actions. Why not try this strategy in HOI2?
Before I can give you any hints you should notice that this strategy is different and dove compared to conventional gameplay of Hearts of Iron 2.
Sweden begins with only a few units on land and a practically non-existent airforce wich in case of war would not make significant damage. However her navy is somewhat powerfull and should be used as a first front line to repell aggression from Germany or the Soviet Union. All the neighbours of Sweden will be at war, sooner or later, which will hamper the trade of this country. Be sure to get enough resources to your pool before the war begins, you should be able to survive without any bigger trade deals during the war.
Concentrating a big portion of Industrial Capacity for producing Consumer Goods might sometimes give an additional factory and increase your capacity.
War is not your biggest strength, with underpowered forces and a too big country to defend it is not wise to engage in war, well, at least not in the beginning.
Norwegian and Finnish support is recommended. Try to send forces and supplies to both countries to help them prevent getting occupied by either Germany or the Soviet Union but do not engage in combat yet.
When Germany is at the brink of an utterly defeat, then you can engage in combat by helping the Allies liberate Norway and Denmark. Joining their alliance for a short time is recommended since you will not only get an economic support by also blueprints for future development.
Good luck and try to avoid a bloodshed!
Use WWII to your advantage
Sweden starts with rather small army and almost non existing air force but they start with good naval armies. This strategy enables you Sweden to become a Major power and also, It's quite fun to play. Remember to enable the option so that democracies can declare War. Also Full IC Take over is recommended You have to Annex Norway, Denmark, Latvia, Estonia and Lithuania before the German or Soviet Union.
The first you shall do is to trade you metal for a huge amount of energy from Germany, German Energy is quite and you don't have to worry about your metal stockpile. Then Trade supply and metal for money from either Soviet Union or another country nearby (I used to make this deal with USSR and The Republic of Spain). If you want, you can also change your ministers.Before you attack Norway, Be sure to produce some infantries (and IC)
Then Move you troops to the Norwegian border and Cancel the non-aggression pact and Declare war. Attack Oslo from the south but don't battle the divsion in Narvik. Wait until it occupies one Swedish province and then march in to Narvik. Once Narvik is yours, Annex Norway. Ususaly the allied don't attack you if you do this quick and early.
After Norway, Wait until Germany annexes Austria and the Declare war on Denmark. Until now, your Infanteries shall be finished. Ferry some divisions to odense and make more troops to attack and occupie Copenhagen and then take Århus before Denmarks last Divison move there.
By now you shall have around 40 IC and a third Techslot (Maybe a forth if you have build IC in your Country) Continue to upgrade and produce more Divisions. It's also recommended if you have som land doctorine, Infantry, Naval and Artillery researched. Now, Wait until the Finnish Winter-war and choose Swedish intervention. Don't send all your troops to Finland as the Soviet will kick your ass back to Sweden and if you're unlucky: You will lose half of you army. Under this time, It's recommended to have 2 fleets of 3 transports ship and a pool of at least 30 convoy ready to launch an assault on the Baltic stats. When the Winter war is over, declare war on Estonia and Latvia. Ferry some troops and take the weakest of Tallinn or Riga (every Baltic stat only got 1 province with victory points) first and Annex one of them first. Then wait until the other capital is empty and then launch a Amphibious assault and annex. When your done with Estonia and Latvia, Move your troops to the border, Lithuania shall be very weakened do to the germen attack on Poland. Declare war immediately and rush to the the capital and Annex.
Now you shall be in the middle of 1940 and you may have around 55 IC right now depends on If you have built IC or not. Upgrade your troops to 41 model Infantry and produce more armies to prepare an assault on Ireland, Yes you can do that from Sweden because you controls the northern part of the Atlantic. You shall be around 1942 when your troops are ready and then ferry some men over to Ireland, Launch an Amphibious assault and rush to the Capital and Annex. Now you got around 70 IC and you're now a Swedish major power.
Either you can stop your conquest here OR choose from one of following: Try to take parts of Northern Germany to Control the whole Eastern sea, Do this when Soviet and The Allies are pushing the German back to Germany, OR Produce some more troops and a better fleet to Occupy Spain.
When this is done and WWII is over. You can choose now to stay in Neutrality or Join either the Allies or (If you're lucky enough) Commintern. Depends on what strategy you're to play you shall choose your side Carefully