Continuing from yesterday, once you have mono mixed your song and located any trouble issues (as well as mixed the song to the point where it sounds good to you,) you should now move back to stereo. Keep in mind, this will change your mix DRASTICALLY and may even make a difference in the levels.
Think about it like this. If you scoop peanut butter with a spoon and put it on bread as a clump, you get a concentrated bite. If you spread the peanut butter, it becomes thin and has less of a presence. How do you fix it so that the song was as good as you had it in mono?
A Mastering tool.
My go-to is iZotope. I normally load it up once my track is mono, and get a good mix there. That way when I jump to stereo, everything is generally in a good place and I can change the level from there. Don't be afraid to mess with the settings! Play with your mastering tool. The best version of your song will be one that you are happy with. I would recommend that if you produced your song, to take a 2-day break before mixing.
Everyone has a different process when mixing. The best advice I have received when it comes to mixing?
Trust Your Ears.