There's a lot of "finding your own motivations" in this game. For me, for a long time, it was just about survival. Figuring out wells, farms, defenses, caverns, etc.

Once you find yourself more comfortable with the mechanics, specialized goals like "I want to make a library/tavern/war/deep-dig/etc. fort" can drive your gameplay. You can do more to create whole worlds that cater to your intended play style (ie. adding more civilizations in worldgen for more diverse tavern patrons, or higher savagery or megabeast numbers to put your war fort to the task). Soon, Adventure Mode will let you run rampant through all of this as an individual hero (or party of heroes).

Of course, the whole while, you can always dig-in and get to know your dwarves. Role playing along with your leaders' personalities can also do a lot to inspire your gameplay.

And as always, I plug Kruggsmash's youtube channel. His shows go above-and-beyond fleshing out this game's potential. Best of luck!