Since this is (somewhat) my specialty, here's my method. First fell all the trees. 1-2 dedicated woodcutters should scour the map in a season or two. As they're working, dig some. 1 good miner (trust me on this) will become near legendary digging out stockpiles. I usually dig a 19x19 underground square, and dig 3 of them on the first three Z levels. These are the first stockpiles (for me, 7x7 plots) and farmland. If you hit rock, then place a dining hall there, once smoothed and engraved. By this time you'll have some trees, so build a wooden wall around your fort. Being the tower-minded and OCD person I am, this is a 21x21 wall for me, which consumes 160 logs (159 +1 door). Now you've got 2 legendary woodcutters and your miner should be hitting rock. Have him expand, dig exploratory tunnels looking for ore. If you're not sure what exploratory mining is, you're pretty much just trying to reveal as little of the underground as possible while still finding ore. For full coverage, 1 wide hallways separated 2 each will reveal all tiles. You can separate further though, because the ore is big and you're not going to miss a whole vein of hematite in a 3x3 square. As you're mining for ore for military/traps/whatever, your one, single miner is going to skill up. He's legendary quickly, and all the stone he chugs through will become boulders. This is important, because above-ground forts consume a TON of resources. A 21x21 tower consumes 441 building materials, and these materials don't come from nowhere. Your average underground fort has stone as a waste resource, but an above-ground will periodically lack stone. You're not naturally digging for it when you expand, so the amount of available stone is based purely on what you quarry out. Thus, fewer legendary miners are much preferred over many unskilled ones.
Also bring a herbalist. Enjoy strawberries. I usually channel out a layer of the surface, then floor over it, giving me an under-the-surface "above-ground" farm plot for strawberries, and another plot for plump helmets. I usually embark without food, as a herbalist can find a lot quickly.