You can use them up to 6 times, as long as they're kept clean. After wearing them, simply take pointy tweezers and pull the leftover dried glue.
I prefer applying the lashes after eye makeup. This way, powder doesn't fall all over the hairs-the result is a cleaner, more tidier look. The eyeliner will also look smoother if the lashes are applied last.
Finally, you can use mascara on them to lift them, but this will shorten their life span. If you're using mascara on your lashes too, you won't need as much- fake lashes provide enough drama on their own. However, I recommend using mascara so as to blend your real lashes in with the fake ones for a more realistic look.