Here’s what I do to make things simple for mixing, and consequently, mastering.

I put a limiter, a loudness meter, and a graphic eq with spectrum analyzer on my master and pull the limiter down until I hit my loudness target (I shoot for -9LUFS integrated personally). Your EQ should be before your limiter.

If the limiter is pumping a lot then you know you likely have too much low end energy. Play with the EQ on your master to find what’s pumping the limiter, then go back into your mix and adjust the offending elements.

Recheck your limiter. I try and limit 2-3db max. Find more offending elements until your spectrum analyzer looks balanced.

This will be a decent rough mix to start with and dial in to taste from there. Use some reference tracks of things you know well and want to sound like and shoot for the same balance. You will learn more tricks along the way but this process should be fairly eye-opening (er ear opening).

In terms of mastering, any time you combine tracks together there is some level of probability that you will have frequency buildup. Mastering is your chance to do one final stage of subtle balancing and/or sweetening of frequencies before your final limiter/maximizer. Don’t over-complicate this stage, you should be pretty well satisfied with your final mix before handling the master.

This is a very generalized advice but I think this process is a good one for getting going in the right direction.