I tend to give high agility/strength dwarves the more critical jobs in my fortresses, such as mining, masonry, smithing, and such. Workers with higher agility/strength will manufacture goods more quickly than clumsy dwarves. I also try to match preferences to job roles, as crafts dwarves with preferences that match their jobs tend to produce significantly higher quality items.
Those dwarves with low agility/strength get drafted. My military, especially in the early stages of a fort, tends to have high mortality rates, so I may as well be losing the weak and clumsy rather than the strong and quick. If they survive long enough to gain significant weapon skills, they will have improved their physical attributes enough that the initial deficit doesn't matter much. The practice of drafting slower dwarves also means that my hauling population will get things moved around more rapidly, as only the average or above speed dwarves remain.
I usually don't pay too much attention to personality traits when assigning jobs, but I try to make sure the chief medical dwarf isn't a procrastinator and likes helping others. If there are several candidates for a job with similar material/item preferences, then I'll usually assign the one with higher creativity and artistic appreciation. I'm not sure about the artistic appreciation trait, but I've read that dwarves with a higher creativity attribute have a slightly better chance of making higher quality goods.
Of course, if a migrant has a high enough skill then it may just be more easy and efficient to assign them to a critical job rather than training someone else up from scratch, even if the migrant's preferences don't match the job and they happen to be a lazy, procrastinating s.o.b.