Deflect and thrust back in one motion. The parry is a small, precise deflection of the opposing blade — not a swat; the riposte follows without a pause.
Parry and riposte belong together the way breathing in belongs with breathing out — practised separately, neither one works. The parry itself is far smaller than beginners expect: a minimal, controlled deflection of the incoming blade, not a swat. Swing wide and you open your own line and take far longer to get back. The second typical error is the pause afterwards: you parry cleanly, enjoy it for a tenth of a second, and your opponent simply carries on. In foil and sabre that costs you, because there initiative decides the point. So drill the two as a single movement, and steer the blade with thumb and index finger rather than the whole arm. What tends to get missed: without the right distance there is no riposte at all. Stand too far off and your answer after the parry is simply too short — the parry was still correct, just worthless.