If you can't make a complete and adequate shield, you have no business sparring.
You should be able to target accurately. Practice targeting BEFORE you begin sparring. If you can't hit your target more than 90% of the time, you don't spar.
Moderate your hits. Begin with a minimal amount of force, and work your way up, so that you do not overwhelm your opponent's shield immediately, and risk harming them.
Favor simpler attacks--psi blasts, drills, small bombs....and not things which might escalate out of your control, such as constructs that self-replicate or spiral up in power.
Do not use nervous system ability, psychokinesis, kinetic ability, or other abilities which might physically harm or even kill your opponent if not carefully controlled.
Spar ONLY in #PsiPractice on IRC, not in the #Psion_Guild channel. Be sure that everyone who is in the room knows what's going on.
This should go without saying, but do NOT attempt to hurt or harm your opponent. This is meant to be practice, not a real fight. Damage done in psychic combat COULD be permanent, if it is severe enough.
Sparring in groups of more than 2 should only be done by those who have completed the classes, gotten to at least week 5 in the manual, or who have an equivalent or higher experience level with shielding, targeting, and psychic combat.