First, you want to make sure the feeder is in a location that’s good for the birds but bad for the squirrels. Squirrels can leap horizontally up to ten feet with no sweat, so the ideal feeder location is away from roofs, porches, trees or utility wires. You should prune trees within launching distance.
It’s best to mount the feeder on a smooth metal pole at least ten feet high and away from any trees or structures, if possible. You should also consider adding smooth plastic baffles above and below the feeder to tilt and twirl if a squirrel hops onboard. You can also enclose the feeder in metal fencing with mesh large enough to allow birds in, but small enough to keep furry creature out.
One last option is to mix in cayenne pepper with your birdseed. Birds don’t mind the heat, but squirrels can’t take it.