This little tip is easy, if you're the one opening a new package of corn starch (or any other dry type of material, which is in a plastic or cardboard container and has a security seal on it).
Instead of just ripping off the seal entirely, cut it in half so that it's still covering half of your container; this gives you something to level off the measuring spoon, ideal for corn starch, ice tea mix, cocoa powder and the like.
I use a serrated steak knife to cut the seal in half, so it gives a good edge.
Scissors won't cut it properly, so use an Exacto or craft knife, sharp razor knife or something similar.
This will give you a way to use an accurate measurement with a measuring spoon or teaspoon, by using the edge of the seal to scrape off the excess powder from the spoon, giving you the perfect level measurement.