"Always keep the arms away from the body.  This applies both to a standing or sitting position.  Performing in this manner provides essential freedom for both the inhalation and exhalation."²

When the arms are held against the body, breathing is severely restricted, cramping the action of the intercostals  muscles that expand the rib cage.  As a general rule, KEEP THE ELBOWS SUFFICIENTLY HIGH AND AWAY FROM THE BODY, much like an inverted V as shown in the above illustration.¹

Just as a trombone player is instructed to "play to the left of the music stand", the best position from which to read for a trumpet player is "through the arms".  Barring a very low downward angle of the horn due to a very receded jaw, reading between the arms encourages the correct arm position, both the right AND the left.  Also, it prevents the player from "playing into the stand" and better still, from "HIDING behind the stand".  So encourage yourself by placing the stand lower than usual and READ BETWEEN THE ARMS!

The left wrist must be in a straight line with the forearm as the left side of the inverted V (stated previously).  This will cause the instrument to be at about a 45^o Angle from vertical.  This is perfectly acceptable.  And the fingers of the right hand work best when FLAT across the valves at the first knuckle from the tips.  As a young child, we were taught to play with the fingers curled and with the tips on the valve caps.  As fingers grow, the right hand will assume too much tension when playing this way as an adult.  Think this point over carefully if you still "play on the tips".  Speed and "snap down" power is sacrificed. As an added directive, remember to "snap" those fingers down, even on the slowest ballad, ala Herbert Clarke and Doc Severenson.