o, what, just put my bedroom like five tiles back instead of immediately up against the side of the hallway or something?
No, think "big picture."
Not "I need housing for 7 dwarves," but "I need to
start housing for 200 dwarves."
So when you decide where you want to start putting bedrooms, look at how much space you have to expand before you even dig. Can you fit 3 z-levels with 50 bedrooms on each in the space you're looking at? Rough it out with the Mining selector if you're not good at visualizing. (I'm terrible at visualization, so that's why I draw my whole fortress out first.)
If you've got the room, then start building in a modular fashion. Dig 10 rooms right next to the corridor and then dig a corridor around them. Then mark off another 10 with expanding corridors. And another. And another. Mine out only as much as you need or think you're going to need soon...but treat the unmined areas as if they're already part of your fortress. Their space is not negotiable.
Adding cross corridors ahead of time ensures you don't end up with hallways 1/2 the length of your fortress with no turn offs and what not.
3-tiles is also the recommendation for corridors. Once your pet population goes up, 2 does not cut the mustard for traffic flow, and definitely not once you break 100 dwarves.
Lots of times, fortress design starts to look like....
. . . . .
. . . . .
. . :::: . .
. . :::: . .
. . . . .
. . . . .
Where the original part of the fortress ( : ), where everything important happens, is a warrens of tightly packed everything, And the rest of the fortress ( . ) is where the designer finally started allocating the space they actually need, both so things flow and so they don't have a seizure looking at their fortress. And because most people
like centralized designs....the heart of the fortress becomes a traffic jam/breeding ground for problems spreading in a virus like fashion. (Fires, targets for berzerk dwarves, ect..)
So yeah, never stop thinking about the overall design of your fortress as you go. It's easy to get sidetracked from design because something happens that demands action RIGHT NOW, so you build emergency somethings which, because you're not thinking about design anymore, you end up building/digging into area you didn't want, then you have reorganize the design you were planning.