I think I mentioned this under sewing pleather, but it is great for any fabric:
When you are folding a hem or seam that is too small for you to easily use pins - use plastic coated paperclips! When sewing pleather at any size they are awesome as they won't poke holes and if used carefully will not leave any permanent marks!
Tiny binder clips will also work extremely well (though they are heavier) but only on fabrics that will not "remember" the pressure areas (in other words, don't use on pleather!).