Squirrel Baffles
The simplest technique to keeping squirrels out of your bird feeder is to simply keep them away. Now this is often harder than it looks, but depending on where the feeder is mounted a simple squirrel baffle can be effective.
Squirrels are great leapers, so you in order for a baffle to be effective the feeder cannot be anywhere near a leaping off point. This means you can't be near any trees or building roofs or overhangs.
The feeder itself needs to be either pole mounted, with a baffle below, or hanging from a squirrel proof pole, that looks like an inverted J. It's critical that for a hanging feeder that the squirrels can't climb the pole halfway up and then leap over to the feeder, which is hanging below the baffle. For that case a pole baffle needs to keep them off the pole as well as off the feeder with a baffle above the feeder on the support hanger.