In just two steps, we took a weak, muddy piano and made it stand out way more in this mix.
First, we removed unnecessary frequencies using an EQ. We don't need the entire bottom end, as the piano is mostly occupying the mids and highs. There's also an area around 300-400Hz which we can cut to help with the boxiness.
Second, we tightened up the dynamic range using a compressor. This will allow it to sit better relative to the other instruments, since the quietest and loudest parts are closer to each other.
A slower attack will allow a bit of the piano's transients through, so it maintains some initial power—having this too fast will kill any intensity.
This example only had a few instruments, but if you're working with a more dense mix, you may have to put more thought into your EQ and compressor settings.
