How can I take my graphic design to the next level?

I'm a full-time professional designer in the early middle of my career -- I have been working as a designer full-time for 15 years.

I create lots of work that I am very proud of. However, when I look through something like a design annual, there is so much beautiful work that it makes me want to improve even more.

I've been thinking about this, and I think I mean that I want to improve in an aesthetic sense (which I know is subjective). I want my design to look more beautiful and pleasing. I'm very confident with achieving the communication goals of my design, and I even like how a lot of my design looks. But I would love to reach that higher level of beauty the masters seem capable of.

What should I do? How do I take my daily work to what I consider the next aesthetic level?