Typically I first create a 20-tile long tunnel with four 10x10 rooms immediately indoors
These rooms are used for:
1) Storage
2) Kitchens, butchery, Dining room
3) Bedroom
4) Depo & mason/mechanic/carpenter/craftdwarf workshops
After my dwarves have unloaded the wagon and disassembled it, I then move intp phase 2.
Extend the entry hallway a few tiles, then build a 10x20 room, and at the far side of the room, a 3x3 stairwell straight down till I find a cavern or magma. Seal it up if I break through into a cavern. If I hit warm stone, start exploration mining to set up lava smelters, etc.
Open up a 40x40 cavern around the first level of the 3x3 stairwell. Start this with a 20x20, and designate it as a stockpile for just about everything but rock, corpses, refuse. After the 20x20 is done, remove the upper stockpile designation, the dwarves will then move stuff from the temporary upper room to the lower storage.
Once the stockpile has been moved, build constructed walls in the 10x20 room where the stairwell down begins, and make it a windy back-and-forth pathway that enemies will have to navigate. Later, this will be filled with many, many traps.
Set the miners to mining five more tiles around the perimeter of the 20x20 stockpile. Build 1 of every non-magma shop around the edge of the stockpile. Build industries close to one another. Loom by clothier by dyer. Butcher by tanner by leatherworker. Etc. Save room for duplicate shops that you know you will eventually want.
Disassemble all upstairs shops and begin using downstairs shops.
Continue expanding the main cavern till it's 40x40, then create noble rooms, dining and dormitory rooms, hospital, puppy farm, cat storage, bird farm, daycare, etc. around this periphery.
Redesignate the original 4 rooms as barracks / training / general defensive. Or use that area as a place to build more death traps if you generally don't have a military. Build another stairwell up from the edge of the big room, and create a pasture if you plan on keeping animals for hair/hooves/horns or a meat industry. I generally build a big pasture underground, then collect a bunch of rocks in a stockpile next to it. Then I collapse the ceiling above the pasture, and have my dwarves build stairs up, and build a ceiling over the pasture, with a little bunker building at the top that I will eventually build a door at the exit, then a wall inside the door to permanently seal the entry unless I have dwarves disassemble the wall later. The farm is typically located next to the pasture, but underground. I'll build a dozen farmer workshops around the farm and pasture, but all underground.
By this point I've normally been in game about 1 year, and have some immigrants. The next steps depend on the fort.
I typically start with 5 miners, the leader with all admin skills and woodcutting, and a farmer.