It's easy to let pride and emotion take over. If the problem is yelling or raising your voice when you are arguing, you can first try to say the same things but in a business-like tone. That means just using a neutral tone, which can take some of the negative energy out of what you say. If what you're saying still sounds bad no matter what, you can use phrases like, "I understand", "How do you feel about ...", "Do you think we could still ...", "Can we compromise by maybe ...".
You also win the argument when you realize you've managed to be successful in neutralizing a potential blowup or even better, in making your boyfriend feel closer to you with your conversational and caring finesse.
Most importantly, pick only the most important things to disagree about. A lot of things we all argue about in the end are not life-changing priorities.