Don’t apply so much compression that you hear buffeting (pulsing in and out) just apply enough to lower the highest peaks the track hits. Particularly drums - which hit hard and can redline your track overall - and vocals, which can fluctuate based on your singers closeness to the mic or their inflection. Apply a light compression (maybe 2:1 or 4:1) to your tracks. For any ranges that don’t matter for an instrument, kill them! Otherwise, the transient sounds in the irrelevant ranges will add to your overall amplitudes, without actually contributing to the sound. Go through your tracks and get a sense for where the key frequencies are - use a band-pass or parametric filter to see which freqs make it sound good. Bass guitar is 100–500 Hz (and, really, much wider in a lot of cases), vocals are 1–3 kHz, piano is somewhere around vocals, etc. Different instruments have different key frequencies, so make sure there is not too much overlap. Make sure your different tracks don’t collide in the EQ.Definitely abide by these, as they will go a long way: Quick searching online will yield some of the following mixing/mastering tips.
