For the first clip of the year - at least a month before the show - I thoroughly wash the horse, spray on Show Sheen, let dry.
And then for the first clip - I use my big old Oster Sunbeam (we call them "cow clippers") -- nice wide blade for just wacking off all that winter wool and actually if you know what you are doing, does a respectable job of body clipping.
But for show clipping, I prefer the Double K. Again, I wash and Show Sheen before clipping. Saves a lot of wear and tear on those blades. And I keep a big supply of Blade Wash on hand, even though I've washed the horse. Keeps those blades lasting a LONG time between sharpenings.