My horse also drags behind me and gets sidetracked at butterflies, haha!
For being behind me, I make sure I have an extra lead in my hand. When ever he gets behind me, I toss the lead behind me - without looking back, you always want to look forward and keep your same pace - so it hits his shoulder. Usually at the first one he comes up to where I want him, then he drags back again. Just keep repeating the process over and over. Horses rely on repetition to learn. Do something once and they didn't learn much.
When he isn't paying attention, I wiggle the leadrope. If he still doesn't come back to me, I wave the leadrope harder. If he still isn't back to me (usually he is by now) then I take me whole and to wave the leadrope to get his attentions. Make sure that there is no hardware on the halter though - you don't want it hitting his face and hurting him.
Hope this helped!! I hear that clint is good, but also you should try looking into Buck Brannaman.