Give'em time. They'll come. Also suggest squirrel proof feeders. I've a yard full of trees, mostly oak, and more tree rats than you can count. I also use suet feeders and had to start buying the suet blocks laced with hot pepper to keep the squirrels out of them.

WAV is also correct that birds are more likely to come to feeders that are either hung from trees or near trees. My feeders that are close to cover or hanging from trees draw a lot more traffic than the feeders on poles with no cover or tree branches near by.