It's just way easier to rack up calories if the thing you're eating is higher in fats. Remember that fats have no fiber (neither does protein, but that's another conversation), so you won't 'feel' as full, which can easily lead to a much higher calorie ingestion rate that you're body won't be able to keep up with.

Another big thing is portion control! You hit on the nose with eating too much of everything. Something else I've done is making myself smaller plates, but also taking much smaller bites and taking a much longer time to finish the plate. I make it take as long as possible. That way by the end of the plate I have a more accurate sense of how hungry I still am or not.

It's tough to summarize all of points of my current regimen since I've pulled bits and pieces from lots of different sources and put some personal experience into the mix.