The ones that interest you the most will be easiest to stick with. I find things just through my general interests and poking around.
Favorite music genre? Listen to bands from different countries and see how they sound. TV shows, movies, and documentaries from other countries are another big one. Listen to the original language, see if it sounds interesting, maybe read a little about it.
Or maybe you know someone who you’d like to be able to talk with in their language. It could be anything. Pick one or two things to try and you’ll get a feel for what you like.