Taking forward steps can be confusing for uneducated horse so I always ask for sideways steps first. Then, once they are able to understand how to turn, I ask for them to move towards me. Using a rope around their hind end, or having someone stand behind them helps them to understand the question better and avoids issues like rearing or trying to get away from the pressure.
When teaching this step, I only ask for one step at a time, before progressing to more. I would expect them to be able to lead properly after half a dozen sessions.