I haven't played enough CK2. I've watched how to play videos, I've played a bit. I marry myself and my heir to people with good stats. I fabricate on neighbors, get frustrated that I can raise levies until after I DoW and so frequently my enemy manages to kill one of my levies before I can combine them. Need to work on that, but I haven't because I just find it annoying.
Most of the time I don't really know what I'm supposed to be doing. Maybe starting as an OPM in Ireland is not actually a good way to play, or maybe I'm trying to play it too much like EU4. Maybe it would be better to pick a midsized realm and just manage it internally for a bit.
CK II requires you to be a little more self-motivated. I usually enter a game with a specific goal in mind like "start as Sergios of Naples and form Sicily" or "start as Zoroastrian and became the Saohysant." I actually don't recommend Ireland because I think it's boring. My first game of CK II was as Theodoros Kaukadenos, Count of Prusa. I recommend playing as an HRE vassal or something of that sort. More interaction that way and I think you learn faster while having a little more fun.