How do I get to the next level of skill? How do I get to the point where I'm making efficient fortresses that are up and running in under a year?
Prioritize.
What is important? Not as a player, not what "you like to do", but to the fortress. For me, crops and security, followed by the 1st caravan deadline. Early on I spend 1 week raiding outdoors for plant samples, and AG farmplots get started as well. I train 1 miner in soil first (no UG irrigation necessary), getting underground asap, and then migrate into nearby stone digs and turn the old area into storage/TC farms.
If I can find iron then I have several suits of steel armor by the 1st Fall caravan, which is great for both security and to boost created wealth for that 1st migrant wave. ~4-6 weeks of Stonecrafting mugs plus reject furniture and mechanisms gets me all the trade goods I want/need (Trying that with Prepared Meals next - we'll see.)
Over Winter, my miner starts serious exploratory mining, and I get a feel for where the permanent fortress will be dug. 1st migrant wave (often Winter, always by Spring) provides ~20 dwarves, and 1 will be my 2nd miner, maybe my 3rd as well. Several others become combat masons (w/ woodcutting to keep them armed) and the projects start.
A lot of what I'm interested in learning first is how to make efficient fortresses, where the work gets done with the absolute minimum of wasted time and effort.
... use Reveal on it, and plan out the fortress on paper before starting to dig.
I'm a big believer in graph paper. 1 square = 4 tiles for general planning, 1:1 for details. As you gain experience, you'll need it less and less, as the patterns start to become self-evident - 3x3 workshops here, 5x5 there, what needs to be walled in and what can be out in the open (based on moods and selective materials, mostly), 3-wide and 2-wide hallways there, etc.