Start with a Name
Despite the old addage, your name says a lot about you. We know that Henry O'mally is Irish, male, and most likely Caucasian, just like we know that Jamal Krew is likely of African decent, but most likely does not live in Africa. Kimiko's parents are Japanese - and although she was born in America, we can deduce that her brother Michael is younger, because his name is of Anglican origin; He was named after his parents became more assimilated into western culture.
Decide Age After the Current Year
This one will not take a paragraph to explain. Children of the 1970's will always look for familiarity to life in the 70's. 80's kids, especially Generation X, were angsty with a very "fight the power" attitude. 90's kids still love 90's TV and will not let us forget Saturday morning cartoons.
This only really applies to stories set in our world, but the year someone was born can tell us a lot about their history. We can deduce what they grew up with. What the media was doing. Who the celebrities of their time were.
Physicality is for the Unimportant
Unless the character you are designing is for a video game, nobody is going to care about his silvery lock or crimson eyes. Save this uniqueness for less central characters - support characters. Don't go over the top or it will end up meaningless, but make sure your less than memorable characters have something worth remembering about them.
Your main character already has our attention. His commanding officer, however, is most recognized by the stink of cigar. His wife should be plain, perhaps marginally beautiful, because we'll see enough of her to form a memory. The sister he rarely hears from, though? Stunning and barely clothed enough to work at a strip joint.