I haven't found any easy ways to deter squirrels from raiding bird feeders, but here are a few things I've found that slow them down.
1) Squirrel-resistant feeders. Large, metal hopper feeders that close when squirrels get on the perch do well at turning away squirrels. Make sure they are heavy duty ones, though, because squirrels will chew through many kinds of plastic, including small plastic windows that show you how much feed is left in the hopper. We also have a lantern-shape feeder with a wire cage around it that birds don't seem to mind going into but that really is effective at turning away squirrels.
2) The long, thin pole baffles work better for me than the flatter, round baffles.
3) Keep feeders well away from trees where squirrels can climb and make death-defying leaps onto feeders.
4) Feed them away from your bird feeders. If you put out food just for the squirrels far away from your feeders, it sometimes will slow down their raids. But it also can just serve to attract more squirrels to the area.