I thought I would put my two cents in here. I'm no expert when it comes to calling elk. I've had some amazing experiences though. Hunting bulls in the bugle is the most amazing type of hunting imagineable. My tip comes more from my experience with Wild turkey calling. I know it sounds like a stretch, but from my experiences a lot of things transfer from turkeys. My tip:
Pay attention to your quarry when calling. It will tell you what it wants to hear. One of the fastest ways to run off a turkey is to call aggressively to a temid tom, or vice versa to call passively to a hot turkey. I think the same can be said about elk. If you hit the bugle and he immediately challenges you, then you should get aggressive. If a bull is rather temid then you need to work closer and make soft soothing calls. It was amazing to me how much calling a big bull was similar to working tom turkeys.