Do your homework
Simply calling up a provider and asking for a better deal is unlikely to work well if you don’t go armed with some information about the better deals you may get elsewhere. Make sure your provider believes you’re going to leave if they don’t do something drastic.
Set your provider a challenge
Get them to match the biggest conditional discount you have found elsewhere. Be clear about what you want to get out of the conversation, and be willing to push for it. Realistically, your provider will have a limit as to what they can offer you — make sure they reach that limit.
You’re far more likely to get a great deal if you’re polite, but also insistent. It’s in your provider’s interest to keep you, even if it means you’re paying less than you were before.