The case for practicing Rock Paper Scissors runs into an obvious objection: the theoretically optimal strategy is to be completely random, so what is there to practice? The objection is valid but incomplete. Randomness is the goal. Getting there reliably, especially under pressure, takes work.
Most players who think they're being random are not. Ask someone to write down a hundred throws and you'll see Rock clusters in the first twenty, a tendency to avoid runs longer than two, and a systematic shift from losing throws to the next one in the cycle. These are consistent human tendencies documented in controlled research settings. You almost certainly have them too, and you almost certainly don't know exactly what your pattern looks like, which is the first problem practice solves.
The second thing practice builds is timing. In competitive play, throws land on "shoot" — not early, not late. Early throws can be read by a fast eye. Late throws can be adjusted to. Consistent timing removes a physical tell that most players don't know they're broadcasting. The way to develop it is exactly what it sounds like: count cadence repeatedly until the throw timing is automatic.
The third thing is opponent reading. The same behavioral patterns that you need to eliminate in your own play are the ones you're watching for in an opponent. Winners repeat. Losers shift in a predictable direction. Spotting these patterns and acting on them within a best-of-seven set is a learnable skill. The more opponents you've played, the faster you recognize the patterns.
Practical practice: track your throw distribution across sets of fifty or a hundred, correct until you're within a few percent of equal thirds. Drill timing with a metronome or steady count until the throw is automatic. Play short sets against different opponents, review what you did, note where you were readable. Repeat.
None of this is complicated. It's just deliberate enough to feel different from the casual game most people play. That gap is exactly where tournament players live.