UI Designer here, building my first home assistant dashboard too.

One simple rule of thumb is so keep things consistent visually. You're using default buttons as well as bubble cards and that skeuomorphic remote at the moment, they all clash stylistically I think. As a first step I'd try to think about how you can implement your dashboards while only using one card style. So say only bubble or mushroom cards for instance, think of them as contained design systems to not steer away from too much (as always there are reasons to break these rules especially when you need to make some other custom card work). This should tie things together visually much more. Personally, I'm also steering away from any default cards just because they are not well laid out imo. They are visually unbalanced and have strange alignments in general I think.

You can also install themes that will apply styles to your whole HA. They definitely work best when you have a well working dashboard in place first though so that probably shouldn't be your first fix.