Making The First Cuts
Many books on the subject of chip carving recommend that you hold the knife in a manner that to me seems awkward and uncontrolled. If you are able to carve that way, go ahead. I feel more comfortable holding the knife like a pen, except perhaps a bit more upright. This feels natural and helps you achieve a consistent angle of cut.
While cutting at the same angle into the wood, it helps to vary the blade angle forward or backward, depending on the type of cut you are making. Obviously, you can't turn corners if the blade is at a shallow angle, so stand it up. On the other hand, with small chips, you can actually cut against the grain by almost laying the knife down and cutting. By holding the knife this way, the heel of your hand is on the work, as is your other hand. The first or second finger of your left hand guides the blade.
If the movement of the blade is away from you, your right hand holds the knife, while a finger of your left hand actually pushes on the back of the blade. When cutting the other way, your right hand pulls the blade toward you, while the finger on the other hand acts as a restraint. Be careful to place your finger just above the sharpened portion of the blade when cutting toward you. For finer control, use your finger as a fulcrum. For example, when you near the end of a cut, stop pushing with your finger, and pivot the knife forward, being aware of the point's location, so you don't undercut.
I carve sitting in a swivel-type armchair, and place the work on a piece of plywood that extends off my radial arm saw table. The work is about chest high, so no bending is required to see details.