Captbillc's description sounds about right to me. The key in my experience is that the top of the mast needs to be quite a bit higher than the normal operating location of the throat. If the throat is hoisting all or nearly all the way to the top of the mast, it is tricky to get enough purchase to get it all the way there. Also, if the mast is not tall enough, it will be tricky to get the peak where you want it too.
Here is a photo of a gaff-rigged pocket cruiser. This design has a particularly short luff, with lots of mast above the throat. It is very easy to get the sail up by simultaneously hauling both the throat and peak halyards, keeping the gaff level, until the throat is at max height, then the peak is raised the remainder of the way: