Depends on the dog in question.
From the top, you don't want them to look like a sausage. You shouldn't have to feel too hard for ribs.
Field Labs can have a severe to moderate tuck-up. Conformation types might have a mild tuck-up or none at all, but in some of the photos I've seen lately from field events, they might have a mild tuck-up while running even if they don't have one at all while standing.