Correct clamped quick release lever direction
There is only really one rule - position the lever such that it is protected from being opened by hitting or snagging on something.

Straight forward or down is not a good idea, obviously. A rear lever pointing straight back is not good either as a collision with the front wheel of a bike close behind could potentially open it. 

Rear levers protected between chain and seat stays is probably OK, maybe more vertically behind the seat stay is better. Front levers angled back and up behind fork legs is probably good. 

Otherwise position the levers wherever is convenient.