The entrance to the fort is a long rectangular room, with a pit at least 10-20z deep with a lead plated floor for extra ouch and connected on both ends by drawbridges. Connecting the two bridges is a single tile wide winding path (with the intent to make it so enemies have to stop sprinting and make turns) that is flanked from the sides by the wide empty pitfall and then fortifications carved into the stone where my crossbowdwarves will pelt invaders with bolts, and if they make a bad dodge down they go. And for good measure I'll have a swarm of warbeasts down there to go tear apart the maimed enemies that happen to survive the fall as well as a backup rock of fortifications, just in case. Access to the bottom room is of course blocked by a bridge and the walls are natural smoothed stone so they can't be climbed. This room exits into the room described below.
The centerpiece of my forts is usually a large central room that is either square or rectangular that is at least 3z high, open, and has natural smoothed and engraved (not constructed) pillars every so many spaces that are continuous from the bottom floor up to the top. The bottom floor is usually linked to the entrance and spreads out to a few hallways that go to workshops. Along the base of the pillars will be statues. The upper levels will have balconies that overlook into the big room all the way to the bottom, one floor is the tavern/meeting place/dining hall, another is an interior barracks, temple, and such. There will be a 3x3 waterfall cascading down through the middle of the room, with 4 wells in the corners a floor in the middle, and floor grates in the others for drainage. Below that, a 3 wide tunnel going to the edge of the map where the last tile on the map is carved into a fortification to drain the water off the map.
Workshops are usually 5x5 rooms with the 3x3 workshop in the middle with the surrounding tiles set as stockpiles for the required resource, and a large linked storeroom for raw materials below, and linked stockpile for completed products above. I'll have a bridge blocked shortcut to closer to the surface where the trade depot is so during trading and when I'm sure it's secured, I'll have it open so it takes much less time to transfer goods. At the surface, I'll have another room lined with fortifications that exits out into a small fort that is the outer most defense I'll make a safe place for grazing animals here with a bridge enclosed panic room to protect the animals. And another secured tunnel leading from here to the kitchen areas as well as a secondary barracks and archer range so my warriors don't get cave adapted. The outer area of the fort will have hanging floor jutting out to keep climbers out and fortifications, just in case. Eventually I may put a roof over the area for added security. I'll have a tunnel that heads to the river and a section of walls built over the river and fortifications and grates to let the water through but block access to anything from the outside so my fisherdwarves can fish in peace.
For FPS, I generally try to leave most of fortress in a 3D box shaped area over the levels so the distances are relatively short to any one area. It's better, FPS wise, to use more z levels than a large area on any one level.