Start by ensuring that the wheel is properly dished and true. The quickest check is to reverse the wheel in the frame drops and then take a look at how it sits. If the situation flips, then chances are good that the wheel is improperly dished. If not, then true up the wheel, ensuring that it is dished properly and repeat the above. If things are still off, then it is time to adjust the stays and align the drops.
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"98% of the bikes I buy are projects".