In agreement with noxlumos, I would add that the positioning of the lead on the dog is important. If the dog has a standard collar, don't attach the lead to the collar since it's to far down the neck towards the shoulders. Rather, a simple loop at the end of the lead or a sliding type collar should be positioned as far up the neck as possible, towards the dogs ears. The sudden "yank" on the lead should be in an upward direction rather than in a sideways motion. This, by the way, doesn't hurt the dog but only adds tho his belief that you are the leader. Take a look at videos of dog shows to get an idea of what I'm trying to convey. The attitude and body position of the owner/trainer is equally important. It's vitally important to convey to the dog, especially a bulldog breed, your postion as pack leader. You must exude an air of confidence, which the dog will pick up on right away. Your head must be upright, not slouched, and stride purposefully, since this is sensed by the dog as authoritative.
If the dog resists and either pulls away in the opposite direction or worse, lays down, simply carry a small sack of dog "goodies" and make the dog come to you in the event of such behaviour (don't take them to the dog as this is seen as rewarding bad behaiour). The dog should never lead you during the walks, but should be slightly to your rear in a true "heel" position. As noxlumos states, the dog, being of an intelligent breed, should learn the correct responses quickly. Best of luck!