We'll take the time to mix it as if it were our own song and if we notice any issues or ways we can improve it we'll let you know. But basically, professional mixing and mastering includes things like correctly applying Autotune, gate, compression, glue Compressor, eq, reverb, delay, simple delay and panning to your vocal and instrument tracks. Mastering includes applying high quality limiters, dynamic and analog compression as well harmonic exciters to the final mix.