How do you think design coordination was done before we started using digital models? 

What advantages does doing this coordination digitally have over previous methods?

My guess is to have some people sit down and compare the architectural and structural drawings manually.

The advantages is huge. Using digital model, system can help find the clashes. Designers can also communicate using markups and show issues. All groups can get in touch with the model digitally.

What strategies can design teams use to find and avoid clashes prior to the start of construction? 

What can be done besides sharing the models digitally?

Design coordination should be a strong help to avoid clashes prior to construction.

Besides sharing the models digitally, if having structural engineers and architectures working together, they can communicate in time and avoid clashes.

At what point in the project development process should design coordination start? 

Is it ever too early?

When architectural design and structural design are finished, design coordination should start. It is never too early to do the design coordination, because coordination can also give feedbacks to designers about how to improve.