Hey, I have to completely disagree with Alexandra here.
Horses learn when pressure is removed so by alternating pulling and release he will learn to stay still even more!
Hold on to the rope and don't pull, just hold at the same tension. When he makes any attempt to move forward, you release. Then you wait and hold until he steps one step, then release. And repeat.
When you apply the pressure start from very light and increase. If you have to hold for 5 minutes do so.
Most importantly when you ask him to go somewhere, maybe away from the grass, and he listens, give him a treat to motivate him to follow you.
Hi! Tessa is right, not going straight but turning him a little will help, also don't let him dominate you, he has to feel that you are leading him and convinced of where you want to go. Don't face him when he stops, look forward and give some unconstant pressure on the rope : pull and release firmly but gently, it is important that you don't exercise a constantly pulling pressure on the rope, he will just get used to putting his weight on it to stay still. To get him pass this bad habit, you can also lead him for a while with his bridle (lead with the reins but pass them over his neck of course). Try to use a long rope : a lunging one. Of course you can congratulate him when he shows no resistance on places where he was used to stop systematically :)
Turn him/ her to the side and then go straight or have another horse walk in front of u the first time