First, I check to see if anybody has any good metal preferences, like bronze, steel, or adamantine. If exactly one dwarf does, they're my starting weapon/armorsmith. If more than one does, I check their item preferences to see if they like an armor or weapon type that I'm going to be making a lot of and give the skills to the one with the best of those (mail shirts, caps, and battle axes are best). If nobody has any metal preference that I like, I usually cancel the embark and do another one to generate dwarves again.
Second, I check the remaining dwarves for people who don't mind helping others, who are moved to pity, and/or who are impetuous. The dwarf who best fits these categories becomes my first doctor.
Third, I look for dwarves who don't have penalties to their healing rate or disease resistance, and make 2 of them novice ambushers; these become my first soldiers. If there are a pair with bonuses to those attributes, great, but otherwise, it doesn't matter much. Also, every other attribute I don't care about for soldiers, because they'll become stronger, tougher, and so on with training.
Last, I look through the remaining dwarves for the person who likes crowds most and make them the group leader/broker. The other two become a mason and grower basically at random.
Since I've only got one category that makes or breaks a group (metal preference), I only rarely have to redo the embark to get a decent set. I don't think I've ever had to redo it more than twice. I could do without even that; none of it matters terribly much, though compassionate doctors save lives more readily and sociable leaders are more likely to hold the mayor post longer, and quick-healing soldiers are more likely to stay alive.