Gaming and Failed Character Arcs

We recently wrapped up our Monsters and Other Childish Things campaign over on Technical Difficulties, and I've been ruminating on my character(s) from the campaign. 

I like the initial concept I started with — a girl and her blink puppy — but that's about where the character stayed over 15 game sessions, at an initial concept. I am a reactive player. I typically have a sense of where my character is and who they are at start of play, then further define them and how they change in reaction to what's happening in game. Instead of having an idea of what they want and proactively making it happen in game. I can, and have, had interesting, fun characters with well-developed story arcs with this method. But I don't consider it a great way to go about these things — more of a bad habit I have yet to learn to recognize the early signs of and break out of.

For me in the Monsters and Other Childish Things campaign, my problem was that it became mostly combat focused. 

In a separate (currently on going) campaign, in the Better Angels system, this is really biting me in the butt character-wise. Character progression in this system happens through 'sin' and I'm not naturally choosing sin as a reactive move. Honestly this is helping  me a lot — since it's built into the system so deeply I've noticed the problem earlier and have a reward mechanism already in place for trying to break out of this habit.

I honestly think the solution is all on me. I need to do some planning before game night. I need to sit down and think through what my character wants and their plan to get it. Or what I as a player want to see happen and come up with ideas on how to make it happen. I need to preplan some ideas for scenes.

I suppose I could do this right after sessions while the story/plot/events are all still fresh in my mind, but I'm usually emotionally wiped at the end of a gaming session. A good one anyway.