What do you want to do? What do you want to build? What gets you excited? Try various things, and pick one that actually gets you excited, and makes you think

What do you want to do? What do you want to build? What gets you excited? Try various things, and pick one that actually gets you excited, and makes you think "wow, this is so cool" - not something that makes you think "well, the market seems to be moving in this direction, so there'll probably be decent money there".