I agree with Jeff that the more carving you do, the better you'll
be. The real key for me is having an exact picture in my mind of
what the finished model will look like
There are techniques which can be conquered through repetition, but
carving is not one of them. Some of us born with the ability to
carve. If you are one of them then things will be easy. If not, then
one must be trained.
One can train himself/herself, or seek a help of a teacher. Obviously
my advice is reserved for those, who are on self-improvement path.
Start with drawing. Draw what you intended to carve from many
different angles and larger than intended carving. Next step should
be modeling. Model your intended carving from clay, or any other
modeling medium. All the mistakes that you make are easily
correctable. When you are satisfied with the results, it is time to
Take negative impression of your model and cast positive in plaster
of paris. This is your master. From then on it a matter of measuring
and transferring dimensions to working medium.
The time will come when some or even all of the preliminaries can be
skipped, but in the beginning it is essential to have the discipline
to do it step by step.