A lot of professional mixes cut out the entire high end (starting from 16000 Hz - 17500 Hz) with a low-pass filter to get out the shrieking. It does deteriorate some of the sounds in a mix, but I think it's worth it. In my track that I submitted for example, I cut out the entire high end starting from 17500 Hz to get rid of the noise my lead and other instruments were producing. This stuff mostly comes from experience though, so keep experimenting and keep up the good work!