In the case of some of the work we've seen, one wonders if the characters which are being written about are people. Some beginning writers use genderless, nameless characters. While this might have been done in some avant-garde writing, this isn't usually the type of writing which is accepted in the SF world. With all the great names in the world, let's promote some creativity in character-naming. Meek, sensitive characters shouldn't scream or suddenly pull out Ninja weapons unless it's a comic piece.
Physical descriptions are appropriate to the piece.
A viewpoint character should not be able to describe himself, unless it's integral to the plot. Physical description of viewpoint characters can be done indirectly, by the reactions of others to the character and the character's own interaction with the world of the story. Omniscient narrators are pretty much on the outs in the current publishing world. The omniscient narrator hops from head to head, from scene to scene and place to place and there is no single point of view or voice, other than the author's. The first-person narrator can only tell what he experiences and knows.