It all started as a simple experiment : how would Bohemia handle the consequences after guaranteeing both Granada and Luxembourg on day 1 ?
After all, nothing prevents Bohemia from making the most of these perks of being Emperor from the start - such as the second largest army in Europe, the ability to walk it through the HRE territory, and some other bonuses in terms of stability, prestige (which also helps keeping Papal influence as it seems), not to mention what you can get by passing imperial reforms. It compensates more than enough the fact that you're landlocked and not very rich in spite of 6 decent starting provinces - all weak points you can fix quite easily with the right strategy.
So, due to this peculiar position that looks so well-balanced between advantages and challenges, Bohemia has always been one of the countries I was most interested in playing (especially once I decided to edit its original map color, which I didn't find very appealing). On a side note, one of my best friends is Czech, and when I started playing EU3 a long time ago, Bohemia was one of my first games so I could send screenshots and entertain him about the fuss I was doing with his country...
The first wars against Burgundy and Castille didn't pose me any serious problem and got me some riche coastal provinces with 2 CoTs. Forcing a PU with Poland and opening a route to the Baltic and Russian territories was also part of my strategy, so that's what I did next. But I hadn't expected the real lucky, game-changing event : a PU with England (it's not so unlikely though. Henry V is bound to die young, and he often does shortly before or after becoming king, so if you have some ambitions in Western Europe, getting that RM with England can be a smart move). I also took advantage of the war with Poland to reduce Lithuanian power, take Kursk and put myself in pole position to fight the Golden Horde.
More wars against Castille led me to also conquer Portugal. In the East I used the Imperial ban CB to get access and cores in the Baltic sea at the expense of the Teutonic order, and started to build a fleet. Colonization opportunites were still very limited though, since I lacked a land connection between m coastal provinces and my capital. Until this happened...
Encouraged by the way things were turning out, I forced another PU with Hungary, collected some good vassals (a bit too much perhaps, but Norway, Scotland, Holland, Brittany and Naples were to prove quite helpful with their fleets in my future European wars)... and spent the next century doing the usual stuff of fighting hordes, crusading in the Middle East and North Africa... and more unusual for Bohemia : exploring and colonizing my way through the Atlantic ocean !
I met some complications in Central Asia with Ming, who was in a conqueror mood in this game, taking provinces in their peace deals with Kazakhstan, to the point they almost reached the Baltic Sea. Many spies were involved in making these provinces fall back to Steppe Nomads, and direct war against Ming was even necessary to dissuade them from coming back.
Other than that, I reached year 1600 telling myself this was really a pretty good game, with no serious issues that could prevent me from getting further...