This article is from the Recreational Figure Skating FAQ, by Karen Bryden with numerous contributions by others.
The best way to find out which way you prefer to rotate is to try a
spin or a simple jump in both directions. You will probably be able to
predict your natural preference simply by noting in what direction you
can perform turns most easily.
If you are not sure what your preference is, picking your stronger
direction can be trickier. Gus Lussi (a famous skating coach from a
few decades ago) recommended choosing the jumping direction according
to your best side on back outside edges (because that will be your
landing edge).If your right BO edge is stronger, jump and spin
You can try to determine your best side by catching a flying object or
hitting a spot with a ball, (try both throwing and kicking the ball,
as spins and jumps require coordination from both the upper and lower
body). Try with both hands/legs. If you consistently get better
results with your right side, rotate counterclockwise.
There are also practical issues to consider: For example, it can take
a lot of nerve to set up jumps in crowded sessions if you are a
clockwise jumper (because you will be going against the traffic) and
there is probably an increased risk of colliding with other skaters.
That can be a good reason to choose the counterclockwise direction if
you don't have a strong preference.
Some people find it easier to spin in one direction and jump in the
other. In these cases it is often advised to reverse the spin
direction to match the jumping direction, perhaps because it is easier
to learn spins than most jumps in the weak direction -or perhaps
because it worked so well for John Curry :-) !