I own the base game for Europa Universalis IV for about 1.5 years now, but I still haven't done much more than the tutorial because it's my first Grand Strategy I ever played and I'm lost in all the different options.
I have read the beginner guide from the Wiki and played the tutorial, but I find that neither really explain what the important stuff is that I should focus on, especially at first. I have no idea how to start my empire or how to keep it afloat. I get lost in the 3 dozen different maps, the dozens of buildings and units I can build and the multitude of countries I can start with. Even when starting as a suggested beginner nation like Castille or Ottomans, I get overwhelmed by the options.
What is a good strategy to start the game with? Assume that I'm playing one of the suggested beginner nations, so either Castille or Ottomans.