Correct stance:  John Lowe recommends that one angles his right foot 45 degrees to the oche with his back foot tip toed (but firmly on floor).  Many other players I spoke to; Dennis Priestly, Dave Askew, Peter Evison and Alan Warriner refrain from recommending a specific way of standing.  The general advice given is to do what feels most comfortable and natural.  Alan does caution against bending too much although he feels that leaning forward should not be too much of a problem.  Roland Scholten adopts a fairly upright (Tripod like) stance.  See picture.  Is this the reason why he hits so many maximum 180s in every game?

Positioning of arm during aiming: I find that ensuring a straight vertical forearm allows for better follow-through and therefore greater accuracy.