What I find is that club players usually volley the same for defensive
and offensive volleys, they have one all-purpose volley so
to speak. What I do to cure this is that we say "Yes" or "No"
as we are playing the points. The net is the dividing line
and any ball below the net is a "No" volley and any ball above
the white band is a "Yes" volley. No has two meanings: no
you cannot be offensive and no you cannot make a mistake.
Yes also has two meanings: yes you can be offensive and yes
it's okay to make a mistake.
What happens now is that the player is able to become his/her own coach
and apply value judgments to his/her mistakes and determine whether it
was a good mistake or a bad mistake. This simple Yes and No verbalization
teaches them to make the correct mental choices and frees them to be more
aggressive on a ball that it is okay to go for it on and teaches them
to be more careful when the percentages are lower. Learn how to say "Yes"
and "No" and soon you'll be saying thanks and better luck next time to
your opponents as well.
Good Luck on the Court!!!