1 - I search for a place where stone is close to the surface and I start digging the main entrance there. I don't like to have my first floor in soil, I want it to be fully usable for anything. I usually designate all the basic structures (stockpiles rooms, workshops, dining room, first dormitory) since the beginning, than disconnect the digging areas and reconnect them one per time.
2 - While the miners are working, I order some wood cutting and plant gathering.
3 - When the entrance is done, I set a temporary meeting area using activity zones in it, to avoid too much bad thoughts about rain, snow, death by excessive cold/heat, etc. I start to connect other designed digging zones, usually I start from the future food stockpile with connected still and kitchen.
4 - After someone eats some of the gathered plants, I set a garbage stockpile and a small above ground farm. It'll be good for booze variety and it's faster to set up than an undergound one (especially because all the miners are busy diggin all the other stuff)
5 - After the food and dining areas, it's time for a large room with two small 4x4 rooms in it, which is the beginning of the workshops area. First furniture and finished goods stockpiles, so that I can destroy the wagon as soon as possible, than wood, carpenter, quantum rock stockpile, mason. Cloth stockpile and a single ammo + weapon + armour warehouse follows.
6 - As soon as the workshops are done, I start making beds, tables, chairs and doors. In the meantime, I start digging the first dormitory.
7 - Once all the stockpiles are finished, I dig a trade depot room near them. Wagon finally slated for removal. Dining hall set as meeting hall.
8 - Other workshops rooms, all 4x4. One per every kind of workshop. I like to design all of them as soon as possible (even if probably I wont' use them for a while), to manage moods. I make other doors at the masonry, so that I can lock the occasional moody dwarf that can't get what he needs. The craftdwarf is the first new workshop, second is mechanic. While the other workshops are designed (waiting for some immigrant with the right job to build them), I make sone mechanisms and maybe some rock blocks (but not always).
9 - I start digging the personal rooms area. I usually like to have some kind of central shaft, so I may start digging it too.
10 - When the mechanisms are done, I design the drawbridge that closes the main entrance and it's opening lever.
Once the lever and the bridge are connected (usually it's late summer or early autumn), I consider the first phase done, it's time to expand the fort. Nobles housing, first phase of the acqueduct, power farm, necropolis, hospital, central shaft (whic will eventually become a statue garden), main entrance fortifications and decorations, underground farming, search for magma, roads, stationary bridges (aka floor, ramps and walls) over gorges if it's the case, etc.