What lead do you use? I always use a standard gun dog slip lead. I like to use it high up on the neck. When he pulls, try a gentle tug sideways to let him know the behaviour is unwanted instead of pulling back against him in some kind of competition. I also find it pays to praise the dog when they are not pulling.
The more I relax, the more relaxed the dog becomes. Try walking without such a tight lead (where safe). The 5 month old bitch I have now tends to pull when she's excited or scared, I have aslo read that it can be a sign of dominance. Patience and practice does seem to work for me