The first order of mastering a song is objectivity. This is also one of the reason self mastering is so difficult.
Music mastering is two focus: Dynamic and Sonic and has two prongs: problems and enhancements.
Listen to the mix while watching a spectrum analyzer to help identify issues. If a problem is found, ask yourself, what is the root of the problem. If it is a specific and identifiable instrument/track, go back to it mix to fix. Do not just apply eq to the whole master, for example.
Ask yourself when objectively listening, “If I could fix one thing, what would it be?” And let this be your guide. Fix in the mix as much as possible and make very small adjustments in the master/overall.
Regarding compression and limiters these are to address dynamic issues. Overall volume and loudness. Compression is better than pure limiter/RMS to increase loudness. Audio compressed is smoother and adds character. A limiter is a final tweak to deliver correct LUFs and TP.
This is not a subjective part of music making. Beware of volume changes as louder easily can fool you as better.
Contact me if you would like me to master or offer insights to your mix.