Mastering can often be a bit of a game of compromise. Our philosophy is to get the mix exactly how we want it to sound. With the popularity of making songs loud there is a bit of degradation that happens when you push a limiter too hard. We often forget that mastering is an enhancement of the mix not simply a louder version of it. When preparing for a master having your mix sit under -6db is a healthy rule of thumb. This is the peak level. Enhancements can be made by using harmonic enhancers. The use of your compressor at this stage should be looked at as a harmonic enhancer not simply a compressor. Though cutting some transients are important at this stage to not over work your limiter. Our philosophy on Eq in the mastering stage is primarily for deductive eq, cleaning up frequency build up. Multiband compression can then be used in conjunction as a means to control individual transients that may be harsh or dull. Doing all these things while constantly observing the changes you've made as to not bastardized the mix your fellow engineer/producer has worked so hard to create. Mastering is not the cure for a poorly done mix and hence we often offer constructive criticism to help songs sound more commercially appealing. Mastering is a small step in the grand scheme of making a record understanding this and approaching a mix and enhancing it will often leave your clients with a better production of their vision.