Here's a little article about grass for sandy soil... top recommendation is fescue as tomf suggested
Also right now, before you plant your seed would be a good time to till in a bunch of compost, composted manure, fall leaves, whatever organic like that you can get, so that your soil will no longer be quite so sandy!
Here's a little bit about grass for shade:
As far as grass types for shade, St. Augustine is a good warm season variety; red fescue or Chewings fescue are good cool season types.
In southern locations, the best shade tolerant grass is St. Augustine grass. The only drawback to this grass is that it must be sprigged or sodded to establish as no seeds are available. It also has limited cold tolerance making it questionable for winter survival in cooler parts of the transistion zone. ---
GRASSES USED / SHADE AREAS
Saint Augustine - Best choice - PLUGS ONLY - NO seeds.
Zoysia (slightly below St. Aug in tolerance / less the further North the grass is planted)
Centipede (works best in high shade areas / high limbs)