As per me a good PPT presentation should cover at least following points.
What is GST?
This should cover the basics about GST. Learn word supply and unlearn sales.
Impact on Cost?
You should cover what will be the impact of GST on business. To which vendors your client should bargain for cost reduction.
One solid example is transportation, as cost will go down due to time saved from removing check posts.
Documentation under GST
Input Credit on GST
Reverse Charge under GST
Intrastate and interstate supplies and taxation
This should cover impact on branch transfers. Supplies included in interstate trade etc.
Exports and Imports under GST