Everyone already have awesome advice, so I will try to fill in a few useful and more obscure details.
1. Trading: Elves can always be robbed. Hit (s)ieze during trade to take what you will. Doing this with humans will bring bad goods and possibly a siege, but elves are peculiar. If they love you they bring optimal goods by weight, which prioritizes light and expensive cloth. If they hate you they bring cheap (by weight) giant animals. Since I prefer tame giant tigers to piles of cloth, I piss off the elves with impunity: next time, just pick what you desire and hit "s".
Surprisingly, this highway robbery actually gives training. Whatever random dwarf conducted that trade is probably now a good appraiser. Go to the (n)obles menu and hit enter over appraiser, the following menu prioritizes dwarves by trading skills, which include less vital social skills (so a master liar will be above a skilled appraiser). You want to find appraise (anything) and after robbing the elves you will definitely have one. As soon as someone with appraise is appointed you will see the value of every item and know exactly how much trade you are giving.
Speaking of which, is your broker drinking when he should be trading? Turn off only broker will trade at the depot, as long as you give the merchants good profits any dwarf will do, and every last one will learn to appraise from the trading experience, so if your broker meets Armok, you will have a few ready to replace him/her.
2. Military: the default menu is alright, but it is a lot easier to make your own uniform and then use it forever in that fort.
Mine goes: Helmet, Chain shirt, Breastplate, Cloak, Cloak, Cloak, leggings, greaves, boots, gauntlets, shield, shield, shield, shield, shield, Melee weapon of choice or, if archer, ranged weapon of choice. Note this doesn't specify materials, so they will grab whatever is best, be it leather and copper or candy. This way if I initially find only copper and silver and later import steel or dig for candy I won't have to fiddle with the settings. Shift+Enter to assign a uniform to a whole squad at one time.
If you get a cool item, like an artifact battle axe, just remember the dwarf name vaguely and find it in assign unique item: this menu is hell since it lists every damn axe, or whatever, in the fort, but artifacts will have the longform dwarf name and should be easy to find.
Remember: multiple shields save lives, multiple cloaks do too: exploity, but still demands making the damn shields and cloaks, and if you are a boss, decorating them elaborately. Exploit turns to awesome, and still more cool than a danger room. (speaking of which, a perfect danger room takes three tiles: armor stand, door set to internal--so barracks can be designated through it-- and permalocked, ten wooden training spears *and only training spears, not wooden spears, or Armok help you wooden spikes* in one spot wired to a mechanism, wired to a lever outside, whole thing should be isolated from pets. babies will have to bite it).
3. Ore is based on luck, sometimes you just can't make steel. Those times you try a fort that wears the bones of its enemies for armor, copper and obsidian blades and if lucky, silver warhammers (which rock anything except giants made of metal or similar substances).
4. Industries in Dwarf fortress are never totally necessary but add complexity and fun. A good clothing industry might just produce enough stuff to keep everybody happy, or produce beautiful cloths in a variety of dyes and with elaborate unique images sewn on every item. As always in dwarf fortress, increases in complexity are available and enjoyable. Same goes for beekeeping and the like.
Glass however deserves a special mention. Glass in incredibly useful if you have a source of sand and magma. With a magma furnace glass can become anything from blocks for construction to trap components, to windows, to barrels. I've decked out forts in glass for everything but beds. Sand never runs out, and if you ever wish for an f.p.s. efficient fort that won't ever demand stone glass is your best friend (your other best friend is clay: never runs out and good for building and surviving)
5. Burial. build a coffin, designate it to be a coffin with q, turn off pet burial with p (I like to keep my pet buried apart from my dwarves/with their masters). If there is no body, or if the body cannot be easily reached a slab made in a mason shop and engraved for the right dwarf in the craftdwarf shop will keep pesky ghosts from rising.