Like any swimming stroke, many people fail to get the fundamentals right as they are so focused on getting quicker with arms and legs! Breaststroke is a little different because the focus of propulsion is the opposite to front crawl: around 80% of your propulsion in breaststroke comes from your leg kick; in front crawl 80% comes from your arms.
The other difference with breaststroke is that you are actively lifting your head out of the water. If you have read my article on head position in front crawl you will know that the higher you lift your head the lower your hips will sink. So how do we effectively swim breaststroke and ensure we are moving forward not up and down?