Good starting point: drop your arms and put your elbows (loosely) at your side(s), lower arm(s) out/palm up. Have someone lay the rod in your hands. Obviously one's going to be on the lower grip and it goes where it goes. Ahhhhhh, but the upper hand is another ball game.
Give an inch (+/-)and that's your place.
Point being ... well, the point of your elbows. Regardless of caster/type of cast the elbows will be 'wider' than your body or
at the minimum, pointed out to get them out of the way. I'm sure there are good casters who've got something else down 'pat,' but 98% of the time that's what you need.