We almost always print on coated paper and don't know what curves to apply to a customer's file to print well on uncoated paper. Any recommendations other than running no curves at all?

Using curves built for coated paper for an uncoated sheet will probably cause the images to be darker, perhaps much too dark. However, running linear plates on press (50% dot in file = 50% on plate) will likely result in an image that is too light, which is why curves are created for different paper types.

In a curves scenario, linear plates would be imaged and then run on press using a "house" uncoated paper stock. Then, curves would be built at the RIP based on that pressrun. On the other hand, if you are using a color-managed workflow where separations are made at the RIP using a coated profile for coated paper, look at your RIP/prepress workflow system to see if there is a generic "Sheetfed Uncoated" profile that could be selected. Alternatively, you could install a "Sheetfed Uncoated" profile from a third-party application (like Adobe CC, which has a "US Sheetfed Uncoated V2" generic profile that has been widely used for many years). Any generic profile should be used with caution as it was created on an unknown press on unknown paper.