Start with the print you love
Every good palette needs an anchor. Pick the one fabric you would be sad to leave out, usually a multicolor print, and let it make the decisions for you.
The designer already balanced those colors. Your job is to pull them out and give each one room.
Pull three colors out of it
Look for a light, a medium and a dark inside the print. Find solids or tone-on-tones that match each one, and lay them next to the print to check.
Squint at the stack. If any two blur together, swap one for something lighter or darker before you buy.
Add one that surprises you
A palette pulled only from one print can feel a little too tidy. Add a single accent that is not in the print, often the complement of its main color, and use it sparingly.
A thin binding, a few cornerstones, or a handful of star centers is plenty.
Try it before you buy
Open the Palette Explorer, start from the palette closest to yours and try it on a few patterns. Swap one color at a time until the quilt feels right, then take the yardage list to the shop.