A lot of people do not realize that body language has a lot to do with leading a horse....big or small. First, when he acts up do you look at him? Also, are you truely beside him or do you get out in front and try to pull him along? In a herd, the look means a challange....a way for a head mare to tell others to back off that they are about to kick or bite. Also, if a horse approaches another horse that they are not familiar with, they rarely do so from behind because a butt shown toward another means that a kick is being thought of and will happen if you approach. So if you look at him you are telling him to back off. Then you get just enough in front of him and he sees that as a threat I am going to kick.
Get your lead correct as others have stated above. Then get your pony at your side with your shoulder even with his neck...not his head. Get him use to forward motion from there then when he is relaxed he will follow you in such a manner. If he is herd or barn sour, turn him around and leave out from the barn herd area backwards. He will quickly think that is no fun and be much more open to following you.