These are the aspects which have been the most interesting to me and I still find myself learning new ways to do things. I won't talk here about common knowledge like equalization, compression or other basic effects. I believe one can easily find all the information he needs in search engines and Youtube.
Instead, today I'd like to write down three mix-down techniques, that I've picked up over the years and which, although being pretty simple concepts, didn't seem at all that obvious to me, until I learned about them.