I like to pop into thrift stores on a regular basis. I have three sections I always check: furniture, linens and china. Linens are one of my favorite things to look for, many times you can find patterns or colorways that just don't get made anymore. Even if the tablecloth is a cutter, meaning it has holes or stains, as long as it has a good portion of usable area it is still useable as fabric scraps. That's why it's called a cutter. Overall, I have had wonderful luck finding barely used linens and fabrics. Look for a thrift store close to older generations, when grandma downsizes you win.
Tablecloths are harder to come by than napkins. Napkins are everywhere and they always have a huge selection, look for a giant bin at your local store. In an age of disposable for the sake of convienence, beautiful napkins make any party a statement. Even in solids, mixing and matching in similar colorways looks effortless.
How do you pick a colorway? Personally, I love brights, so I make sure it is bright. In my head all brights look gorgeous together no matter what, think Kate Spade. If you love blue, choose all napkins with blues, they will match easily even if they are patterned, think blue and white china. If the thought of mixing patterns is frighening, just think about what you love. If you love each piece individually, they will be great together. Really. It might be crazy eclectic, but it will still make your heart jump, I promise.
If you find three of a kind, like these yellow roses, (I was born in Texas so these are equally crazy and awesome) grab them, especially if you do tabletop photography. It doesn't matter if you don't have a full set, they take up very little space and are easy to store. Read: easy to hoard. I have very little storage space, so I try to reuse props over and over. Eventually you have to get something different for the sake of changing it up, napkins are an easy way to do it. Unlike cake stands, you don't need an entire closet to save them and won't feel as bad putting them in the yard sale.
Is there anything you keep on hand in a large assortment? Wine glasses? Silverware? Plates?