What is the best approach to obtain a great bid from a GC when
constructing a commercial building?

Here is a site with many links that might help you:

http://www.constructionsourceinfo.com/construction/commercial_construction_project_sample_schedule.html

For the price of your question, you may have to be satisfied with free comments.
Very generally, when asking for bids, the more precisely your
specifications are defined, the better and more comparable the bids
will be.