I usually start with the fabrics. I put them up on my design wall and look at them, arrange them in different combinations, and begin thinking about shapes I'd like to use. Then I start cutting and putting things up on the wall, playing around until I like the arrangement. Sometimes it helps to take a photo and look at it on a screen -- either the computer or on my phone-- something about seeing it on a screen helps me see where I need to make changes. I'll play around with different arrangements for a few days until I'm happy with it, and then sew, taking segments from the design wall and then returning them there.
While I do sometimes use my EQ (I have an old version 3) or paper and colored pencils, I very rarely work out the details anywhere but up on the wall.
I think everyone develops their own process, so try out several methods and see what works for you.