It has been years since I got to hang out at the local tobacconist, but Mixing was not so hard. Smell the blend and smell a dozen more and say to yourself, I like this one, but it would be nice to have "whatever" in it. My favorite was Staghorn with Honey Clover in it. Staghorn was campfire smokey, and honey clover was black and sweet. The two complimented each other.
Don't let em scare you. A quarter ounce of this, a half ounce of that. Don't blend a lot of anything till you get it right, then blend several ounces or pounds. With the high price of tobacco, smaller test batches are better. My Tobacconist had 3x5 file cards that he kept special blends on. I have a diary of my cigars and blends and from which source.
Relax and enjoy.