I guess the first step of getting rid of your stash is to go through it and see what you actually have. I tried organising everything when we moved to this apartment in December, but since then I've been lazy and the whole system I had created has gone in total disorder.
So I took everything out and started bagging the yarns into Minigrip bags. Same sort or similar yarns together; lightweight yarns into one box, dk to worsted into another and bulky yarns to a third one. There are two more boxes for yarns that are for the projects on my to-knit-list: the yarns I am planning on using on specific projects went into bags of their own, so that it would be easy to find which yarns were intended for which project. I printed out pictures of the intended projects and put the photos into the bags with the yarns. The yarns I'm currently using or I'm going to use next went to the top drawer of my dresser, so that they are easily available.
I also started a "planning book" to keep up with my ideas and small pictures I draw. I'm not good at writing down my thoughts and find it easier to doodle things. Also Ravelry doesn't really allow you to queue projects that aren't already on Ravelry, so it's impossible to keep track of the things you want to improvise or design yourself. So I wrote down the names of the projects I was going to knit, what yarn and how much I was going to use, and drew some little pictures next to each entry to remind myself what I had been thinking.
Today I've also been dyeing yarns, and finished my lace scarf, but I'll tell you all about it tomorrow.