It's "gestURes" not "gestRUes", but apart from that, the sentence is OK. You could optionally change GESTURES to GESTURING, and WHEN to WHILE, and remove YOU ARE, i.e. "Reduce your gesturing while speaking". This sentence would only be used with a specific person who gestures too much while speaking, and therefore should REDUCE their gesturing. It is not general advice, because it assumes that