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

Before digital models, design coordination was likely done on-site for the most part, but before construction, it was done by drawing out hand-models, revising them also by hand. This would have been very inefficient because for just one design change, the all drawings which all parties had would become obsolete, and the drawings would either have to be done, or they would be annotated.

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?

Teams could first of all spend more time co-designing critical locations or spaces (ie with complicated MEP); one strategy to achieve this is to create a co-working space so that all members of the design team can easily address questions and work together. In these spaces, teams can have regular sit-downs to evaluate any clashes and to quickly and collectively discuss and agree on solutions.

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

Is it ever too early?

Too early is the point where the design concept itself for the building is not quite firm. The design coordination should start ideally after the architectural design is decided upon, and right as the first structural and MEP designs are created.