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Getting your boat to behave exactly how you want it too is mostly just down to practice, but understanding exactly what prop walk is, can help.
Most people do not know why the boat moves sideways in reverse other than it is something to do with the prop.
The truth is, it is nothing to do with the prop itself. It is caused by the downward angle at which the prop shaft leaves the boat and the hull shape around it.
Yachts with a sail drive experience almost no prop walk as the prop shaft is aligned horizontally.
Lets take a yacht with a prop shaft sloping downwards as it exits the boat.
When the prop spins, a rapid flow of water is forced away from the blades. The flow of water is not contained so the spinning blades results in the flow twisting and rotating out at the edges.
When in forward, this heads off on a slight downward angle towards the rudder and has no effect on the boat.
When in reverse, this flow is sent up towards the hull. The flow of the water on one side of the prop shaft is twisting off away from the hull towards the deep and on the other side is twisting up into the hull. This results in a greater force and flow of water over one side of the hull causing the boat to move sideways.
It is important when controlling a boat under engine to only use bursts of intense throttle and then back to neutral. Do not leave the engine ticking over in drive, forward or reverse. You should be drifting or adjusting.
This means you limit the time the rush of water is pushing the hull sideways in reverse and gives you a kick across the rudder in forward to spin the boat without it moving forward.
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