I always start on a brook, almost immediately get 10-20 waterwheels going along with stockpiling a bunch of fish.
The I dig down and start carving out my machine layout. After many forts, I've pretty much came up with the most efficient, least dangerous layout. After I get it dug out, I start building my arc furnace (ALWAYS start with the heavy machinery crate), sorting machine to sort out the bars, and a stonecutter to make some blocks, set up a stockpile that dumps all rocks into the arc furnace, then basically it's "done enough".
Then I'll set up some more waterwheels on the surface and hook them to a drilling rig that tunnels down into my 1 wide underground entrance. With enough power, the drilling rig is sufficient to stop all but the largest sieges.
And then it's time to start a militia and make some gadget gear.