First, many undergraduate music programs have some very specific recommendations for incoming freshemen.   One I know of in the state recommends reading, music theory study, and websites.  It would make sense that any student wanting to get a head start would want to find out what system and what texts were used in their prospective college.  I would imagine that anyone teaching freshman theory would be very happy to provide some direction.

 

Second, any singing in a good choir could be helpful.   Find a summer choir at a community college or a good church choir or even a music camp.

 

I got high marks in undergrad ear training and sightreading but there is nothing like singing in a choir for another thirty years to get your reading in shape.

 

 

Rob