I have one more tip: mixing in mono. Not every time but from time to time it is useful to test mix in mono. In this case we can much better 'see' a masking effect and overal sound 'picture'. In mono it is easier to compare loudnes and selectivity of instruments. Imegine yourself two pencils. One by the left monitor and one by the right monitor and try to compare which one is longer? Then take them side by side each other and do the same compare. When is it simpler?