Step 1: give your ears a rest. Mastering can be seen as the final touch, like a lead editor’s marks before a book is published. If you’re mastering your own works, you’ll need fresh ears to identify what you’ve missed. You can also look at a frequency spectrum analyzer to double check the balance. Sept 2. See what’s needed in the macro picture. Too bass heavy? Mids get lost? Could use more stereo imaging? Here you want to balance, eq, saturate, compress, whatever you feel will elevate the track. Step 3. Levels. Usually mastering engineers will work in Lufs, not rms, and online lately streaming services will tell you -14 lufs, but that’s not really accurate. Use reference tracks here. My opinion though, once you get to -6 lufs you’re potatoeing your dynamics. Theres a balance between loudness and dynamics that you want to maintain. Look at your loudest and your quietest parts. You will want a true peak and final gain at -.1 to-.3 is fine. Really what you will want for mastering is final big picture touches and perceived volume cohesiveness with other tracks of your genre.