Contrary to historical events, Poland-Lithuania begins the Grand Campaign in an excellent position geographically and economically, with rich lands and great opportunities for expansion. Poland-Lithuania’s eastern borders are secure—Russia will never declare war on it as long as they’re allied. This leaves Poland-Lithuania’s troubles to be (broadly) Sweden, Prussia, and Austria. Sweden’s lands are rich and it is diplomatically isolated; Prussia is small, but dangerous if allowed to build up and expand; Austria has an interesting unit lineup, a fairly large empire, and many allies.
Although it is mostly thoroughly average, the Polish-Lithuanian army has some unusual characteristics. It is one of the two major factions that may recruit Kalmuks, bow-wielding cavalry that act as early dragoons and can be useful against melee infantry, as well as the only faction that can use Winged Hussars, some of the best heavy cavalry in the game.
With the Elite Units of the West DLC, this faction also gains access to the Guard Grenadiers, the best grenadiers in the game. However, only one regiment can be trained, so be strategic in deciding where to deploy these guys. The rest of the infantry, including line infantry, is unremarkable. This means Poland-Lithuania at a disadvantage against Prussian and Swedish armies of equal numbers.
The Polish-Lithuanian ship roster and artillery roster are completely standard, with no surprises to speak of.
Prussia is probably the easiest to take out. Its lands are few yet rich, allowing a well-organized Polish-Lithuanian army to quickly knock it out. This is a good course of action as Prussia can grow to be very dangerous if given time.
Sweden is a very large power, that much is true, but Poland-Lithuania’s allies (Russia and Denmark) should serve to tie down some of Sweden’s troops. Taking just Stockholm is enough to permanently cripple Sweden’s ability to wage war, and it is an extremely rich region to boot. It may be beneficial to let Sweden take Norway first so that you can capture it later.
Austria is probably Poland-Lithuania’s most dangerous enemy: it is wealthy, and shares a long border with Poland-Lithuania. Declaring war on it risks bringing Great Britain into the conflict, which can be a very bad idea. Thankfully, war is near-inevitable as the AI usually directs Austria to declare war on Poland-Lithuania in the first few turns. Failing that, declaring war on Bavaria usually causes Austria to enter the fight without involving Great Britain. Austria can be tough to kill due to its vast lands and Poland-Lithuania’s relative isolation in this area.
Beyond pacifying these neighboring nations, Poland-Lithuania may possibly come into conflict with the Ottoman Empire, although this is unlikely to be a major factor due to the Ottoman Empire’s abysmal starting unit lineup and its relative distance. In fact, allying with the Ottoman Empire could be a good idea, diverting Austria’s troops to the south while its empire crumbles in the north. Russia may eventually declare war on Courland, a Polish-Lithuanian protectorate. If Poland-Lithuania is still dealing with multiple enemies, it may be best to simply break alliance with Courland. However, if its enemies are subdued, then Russia’s declaring war on Courland presents a good opportunity to further expand Polish-Lithuanian holdings.
In the west, Poland-Lithuania’s protectorate of Saxony is often attacked by Hannover and Westphalia. Standing by Saxony and declaring war on these minor factions can be a good idea as they are relatively easy to kill, have wealthy regions, and gives a good reason to invade western Europe without offending anyone important.