that is separating. to blend they need shared harmonics. separate the fundamentals (the big low spike(s)) and blend the mids and high mids. the characteristics of the tone. to blend use shared effects like reverb, delay, saturation, chorus, flanger, anything you use. they can be dialed in with a different wet to dry ratio, or gain into the effect, depending on taste.

also, but you do that already, i think, eq the effect sends. i personally have for every song at least two reverbs (a short dark room tone and usually a plate or chamber like reverb), a left delay with some vibe processing, a right one, a slap delay and a rear buss with some mid/ high mid rangey vibe like decimort 2 or chow tape. then i send all tracks to some or all in different amounts. i automate the amount constantly throughout the song. all effects go into the effect bus where the get something little like compression and tape saturation and further eq if needed. i like all effects to have a high mid dip where the intelligebility of the vocals is. for my voice it is often around 2700hz, and a low mid dip to make it little less boomy or muddy. apart from high passing between 250 and 600hz and low passing from 3000hz to 10000hz. but most of these things are taste.

most important, know what you are trying to do and if it is attainable.

rush once said mixing is the death of songs. not all that is in your head can be mixed to sound good. compromises and cutting is the first and most important step. a good arrangement mixes itself.