Each airplane has an appropriate speed and time to have its gear down. Usually you lower the gear in the downwind leg, as you go reducing the speed down to Vref for the landing flap config. In a straight-in ILS approach, you usually lower the gear not after passing the outer marker. Reducing the plane's speed using gear and flaps is in fact an art. The ideal approach is made with idle thrust, from the top of descent down to the final approach fix, where the plane should be full configured for landing, at its VREF and with the engines developing power. The "art" is to start the speed reduction in a mannet that the speed is slowly decreasing as you add flaps and gear. If you lower the gear too early, you'll have to add power to compensate for the increased drag, increasing fuel consumption.
In the Airbus, we usually start the speed reduction from 250 Kt at around 7 miles from the Outer Marker, or 12 miles from the runway. We first select flaps 1 at a speed below 230 Knots. Then when the speeed decays below 200 we select flaps 2. Then gear down, flaps 3 below 185 and flaps full below 177. The plane should be fully configured for landing at the final approach fix, or at final and no lower than 500 ft in a VFR approach.