how do you work on aesthetic and good lines?

By not adding too much mass.
Cutler looked good before he upped the doses. Ronnie looked great in his first couple of Olympia wins. Yates was fantastic pre-belly.
If you go back a few more years, you will notice that Labrada started to look a little worse at the end of his career when he started to add just a little bit more mass. The classic example, in my opinion, is Samir Bannout who never looked the same after 1983 when he put on a bit more muscle.
They are just a few examples of how you can not work on aesthetics and good lines....