By this, I mean, do you open up photoshop(or whatever) with a project in mind, or do you just jump in & see what happens? I usually just open it up & see what happens. Usually I scrap 70% of what I do, because I don't like where it is going. Also, I usually do the stuff in one sitting. I rarely go back to a project. How about you folks?
I just choose a pic and make it up as i go along!

I don't do much editing at all, because it usually becomes awful when I make it. Most don't come out well.
i usually open up the progs when i have a subject in mind, i try to have the image worked out inmy mind before hand, but it most likley changes completly by the time i finnish it, lol, the only thing that stays behind is the main object of the sig, like the car in my current sig
I open a new sig document and pull together some renders that I thought about using.. Opens those beasts up and create a background and place the images on the sig background...I usually have it visualized in my head though.
well, my thing's photo manipulation, so i usually browse through a lot of pictures until one screams to be 'shopped.
I have never considered myself an "artist". Any work I have done has been recent and is exclusively sigs and avatars not to mention is always animated (at least to an extent). I fall in the same category as Fragger however, photo manipulation. I just scan through photos until something comes to me. BTW, I think you sig is awesome Fragger!
I decide roughly what I want to do, usually see something on these forums or others on the web that inspire me to try something similar.
One thing I ALWAYS do is start from scratch, I never use images except renders, the rest is my own patterns or brush strokes. Using an 'original' isn't as fun and isn't as satisfying once you've finished knowing it isn't all your work.
Mines pretty much a combo of both: Usually I have something in mind, but it always ends up being totally diferent. I also used to use the downloadable brushes, but now that i've gotten used to PS its all about filters and patterns.
I just experiment, usually when I make good stuff it's because I'm having fun with the software. Not that I make many good things.... ....