I like them to be about 4 feet long and at least 8" wide so there is enough room to layout the stock where I want. A little variance on those dimensions will work, but limits your layout a bit.
Grain should run back to front, but is most critical to run through the wrist area and magazine are in reasonably straight lines to match the direction of the stock if you are going with a boomer. Lesser recoil require less critical layout IMO.... but you definitely don't want the grain to run perpendicular to the wrist or action area or you will regret it...
Try to avoid sapwood... some guys actually like the look of some sapwood in the stock, and it isn't really weak in the sense it would ruin a good stock, but most guys will shy away from a stock with sapwood so it would be hard to sell later.
Other than those basics, a picture would help as far as further advice...
