Hints for training your cocker to walk on a lead without pulling.

Our 8 month old cocker spaniel is very lively and loves exercise. We can take out to a big grassy area to have a good run around but we would also like to take him for long walks. However he pulls constantly on the lead, has his head down sniffing everywhere, making a not very pleasant experience for us all. Have read books etc to get advise but wondering if anyone has any good hints relating to cocker spaniels.