Bosting in: the big forms and their relationships, first. I use the standard approach that I use elsewhere on this site: working in from high spots. The more time you have spent preparing, pictures, drawings, model etc, the easier you'll find it to visualise this important stage.
I'll also introduce a new carving technique, which I call 'bursting'!
The 'patternmakers vice' sits on top of the bench and is a metal equivalent of the old carvers 'chops'. Sitting like this the work is lifted up to a good working height and, being narrow, you have good access to the carving. I used this vice in the Koi Carp here.
If you don't have this sort of vice, no problem, but you'll need to improvise a bit with your normal bench vice. For example, screwing a block to the underside of the backing board that will hold the carving via a paper sandwich; this bock, or post, you can hold in a vice to lift the carving to a good working height.
You'll find them quite readily with an internet search for 'patternmakers vice' or 'vise'. Here are a couple of sources (in which I have no financial interest):
Search for 'woodcarvers chops' if you'd like to look at the traditional wooden version.