So you've got the most basic short, blue, denim overalls but you're not sure what shirt to wear underneath? Go with a striped shirt. Navy or red versions always look classic, and they'll pair well with your starter set of overalls.
Don't assume wearing overalls means you're commiting to a baggy, more boyfriend-y silhouette. There are tons of options now that are more streamlined and sleek, especially in the longer, non-denim versions. Look for a slim fit with a wider leg, then pair it with simple heels and a basic top. It'll look very '70s glamorous.
turn up overalls, $59.40, river island, asos.com; "lanie" stacked heel sandal, $225, jcrew.com
When to Mix Prints
Shorteralls or shortalls or whatever you want to call them: when they're printed, go ahead and mix prints.