The height-velocity diagram can be found in the Pilot’s Operating Handbook.
The diagram shown here is for a Robinson R44 helicopter, but they’re all very similar. The idea is to stay out of the shaded area. Generally speaking, you want either altitude or airspeed — or (preferably) both. Hovering in the 10-400 foot range puts you inside the “deadman’s curve.”
The height velocity diagram also clearly shows the recommended take-off profile.