Bird Feeder Advice Anyone?

Here's a photo of a House Sparrow. It seems my back yard is over run with House Sparrows and Doves and squirrels.. But very little else seems to visit. I'll ocassinally see a Blue Bird or Cardinal but thats really it. I'm using a standard Home Depot mixed bird food in one feeder and another feeder has just Sun Flower Seeds.

Any recommendations from the experts out there? I'm considering getting a bird bath but don't want to make another bad investment that won't attract anything besides what I've already got.

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What sofjan said plus NO CORN. Corn attracts squirrels and racoons
Bluebirds are primarily insect eaters. Most wildlife stores will have mealy worms(think that is what they are called) that will attract bluebirds.

Suet blocks will attract many birds including most woodpeckers.