I have a project(A) that references an assembly from an external project(B) class library that is located in another vs solution.
I have yet to understand how i can efficiently debug the class library from B while running the program from project A. Is there something I have to enable on project B such as debug info etc so I can step-into at debug time from A?
Try disabling Just My Code (JMC).
By default the debugger tries to restrict the view of the world to code that is only contained within your solution. This is really heplful at times but when you want to debug code which is not in your solution (as is your situation) you need to disable JMC in order to see it. Otherwise the code will be treated as external and largely hidden from your view.
EDIT
When you’re broken in your code try the following.