What actions can I take to stop taking my boyfriend for granted and what can I tell him I plan to do so he feels assured that I've taken this seriously and am trying to change and resolve the problem?

That highly depends on your mutual understanding and connection. For not taking him as granted, you need to accept the fact yourself first that he is not for granted. A few words of reassurance and affection can go a long way. Try to spend more time with him, go out together and make him feel that you are there for him when he needs you the most. That being said, actions will always speak louder than words and you being there for him will speak up for itself. Even though at times, it might feel like pointless, but over time, it will help you stabilize your relationship. Goodluck!