For SSP, you really can make no external modifications, beyond the sights. You can stick skateboard tape on the frame, but no stippling, grip reduction, etc.
I'll second (or third) the recommendation of improved sights. Fiber-optic fronts are very popular, combined with a plain black rear.
Trigger parts are available from a number of sources, but some very good shooters use a stock trigger.
For ESP, you can stipple, reduce or reshape the frame and trigger guard, add a magwell funnel.
The IDPA rule book is currently undergoing revision, so I wouldn't make many changes based on what is in the current rule book. That has been revised over the years, so there are some current rules that vary from what's in the book.