It depends on the types of birds you want to attract. If birds abandon your feeder after months of use, it's time for a cleaning. Use hot, soapy water and add a cap of chlorine bleach. The species you attract is primarily determined by the seeds you offer. Black oil sunflower seed is the all-time favorite of all the birds that visit tube and house type feeders.
Squirrels love it too.
Safflower seed is a good choice because Squirrels don't like it. Many seed blends contain corn, milo, wheat, red millet and canary seed. These are Not favorites and you will see the birds kick out most of the seeds to get to the sunflower. The most effective way to get a large variety of birds is to put up separate feeders. Perhaps a tube feeder for thistle and another for sunflower.