Re: Harness vs collar
I always recommend people walk their bullies on harnesses and not collars. Bullies have very short respiratory tracts and pulling against a collar can put a great deal of strain on their throat and lungs and make them pant hard. I recommend the Walk In Sync humane walking harness. It fits great, is very comfortable and secure for the dog, and helps to reduce or eliminate pulling. The company also has tons of great training videos to help you learn how to teach your dog loose-leash walking.
Make sure you're not pulling on the leash, or the dog will resist. Try to keep the leash loose and encourage the dog to follow you by making silly sounds with your mouth, or using a food lure. Some folks like to toss food treats on the ground out in front of the dog to encourage walking forward. Any of these should work!