Keep in mind also that the coach probably knows more about your son and the others trying out for the team than you give him credit for.
Also as a freshman the make up of the retuning team members will dictate what his chances are to make the team.
There is no shame not making varsity as a frosh---being on JV will probably give him more innings on the field which is critical at this point
There are no tips other than allowing the player to let his talent or lack thereof help the coach make a decision