Low RPM warning with high collective
The key of flying the huey, IMO, is being gentle with the control inputs. It takes time to get used to the movements you have to do to perform the maneuvers.
For instance as you increase power yo have to input left pedal to compensate for the torque, if you lower the power you have to release left pressure
If you hear the low rpm warning lower the collective just a tad bit. Also making abrupt cyclic movements can make the rpms go low. Just make small movements.
With some practice you will get used to it and will start loving the Huey as much as I do.