Trimming Back My Lilac Bush

Our yard has had this lilac bush since before we moved here. I used to trim it back regularly, but the following year there would be few flowers...

A few years ago, I learned that one can trim at least a third of the branches in the center of the bush every year without disturbing the blooms.

I've done that for two years now. As I look at the lilac bush now before the leaves have begun to sprout, it's easy to see which thick center branches I'll be aiming to eliminate this year!