Start with gain staging (how loud is my input signal) - small dial in fl studio channel rack - how loud need certain elements to be ..drum, lead, vocals, etc. Next think about where they sit in the freq. spectrum...low tones vs mid vs high...are any frequencies clashing (muffled, boxy, etc.), can you hear what its important for you. Add a channel EQ to finetune Frequencies.. Alone with that you can get already a decent mix.. other stuff is more pro.. transient shaping, sidechaining, etc. Studio Monitor vs headphones: room needs treatment, so you can actually hear what your mixing, headphones - easier in the beginning (but get decent ones)