1: In the vast majority of cases, I work on odd numbers. Halls are 1, 3, 5, or so on squares wide, rooms are 3x3, 5x5, 11x11... you get the idea. The lone exception: 2x2 bedrooms are employed if I'm afraid of vampires, though more often I'll use 1x3 "hall" bedrooms
2: Workshops are built in "Cozy" rooms -- ones that fit them directly, so most shops go in 3x3 rooms with siege workshops on 5x5's. They have one entrance in the center of a single side, and a door is placed in the entrance. I started this practice because of failed moods, but even now that it's a really, REALLY rare event I keep on with it.
3: NOTHING is built in soil if I can avoid it, with the following exceptions: Farm Plots, Farmer's Workshops, Screw Presses, and Querns/Millstone for actual buildings, along with pastures and digging out soil layers for tree farms
4: I don't do metalworking without magma if I can avoid it. Non-magma smelters & forges are only built if I decided to embark with tetrahedrite instead of a pick, or if a metalworker moods before I can set up magma industries. In either case, they're promptly deconstructed when no longer required. The same goes for Glass and Ceramics.
5: Everything gets smoothed. If it's practical, everything is engraved too, but if I hit soil on a layer where I wasn't expecting it (
) I'll just keep it smoothed for the looks, since constructed floors can't be engraved.
6: Basic Dwarven amenities are a 1x3 or 2x2 room with bed, stone cabinet, and stone coffer, and a 1x1 tomb with stone sarcophagous. Dining halls are communal
7: Elves are treated decently when they come to the fortress. They may be horrible, hypocritical, people-eating maniacs, but they let me turn my XXclothesXX into Giant Monster Cage (Highwood) (or a bin of new cloth), with is too useful to pass up.