Swatches
I've just started working on a new piece, and snapped a photo of one of my favorites parts of the process - working out the color palette. If possible, I'll lay down the swatches on scrap pieces of the actual paper I'm using (in this case, black Colourfix). If I like the color, I'll put the pencil aside into my "palette box" for the picture. Hopefully I'll also remember to label the color - something I don't always do when I'm rapidly trying many colors - so I can reference it later on. It's also a nice sanity check to look at all of the colors in the piece at once as swatches - if they have good harmony, then I'll feel more confident about how the final picture will look. Here's the pic of the working palette for my new piece: