If you're planning on a mid-century modern front door or garage door re-do, you should definitely read this article, or at least the first three pages of it. It focuses on Eichler doors, which makes sense since it's on the Eichler Network site, but the basics can be applied to any mid-century modern home or atomic ranch.
For the front door, keep it simple and modern. Go plain with a pop of color, interesting mid-century door hardware and a large mid-century door escutcheon. Or buy a Crestview Door. I'd suggest using a color that pops and mid-century modern door knobs on a Crestview Door as well (as evidence by my front door above).
For the garage door, they suggest a color that matches the main color of the house or the trim in order to make the garage door look like it's part of the house. For Eichler garage doors they recommend vertically grooved wood, which were original of Eichler houses. A vertical grooved pattern could look good on any mid-century modern garage door .
It's a pretty simple rule of thumb: make the small door pop, make the big door look like the house.