the manager in the recording scenario must monitor the budget, must aid in the set up of the recording date(s), must be encouraging but not obsequious. and, above all, must know when to stay out of the creative discussion.
for live performance, again, constructive criticism, but mainly making sure the promotional set up and follow up of the date is taken care of.
I am also in the field of managing. Im a college student as of now. But I think the most important aspect of managing artists or labels is contacts. You must be everywhere with all the resources. If you have any product or music to promote join one of the Performing Rights Organizations like BMI, ASCAP, or SESAC. Most of them offer limitless resources to the industry but you have to pay for it.