Now that you've made your own homemade starch, there are some tips that will make your ironing look professional:
Always use steam in your iron when using homemade starch.
Let the starch absorb into fabric for at least 30 seconds before ironing.
Clean the bottom of your iron after each use.
White marks on clothes when ironing means you are probably ironing too soon after applying the spray starch. It's also possible that you may need to add a little more water to your homemade mixture.
Starch will not only add body to your shirts and blouses, it is also a layer of protections between your skin and collars and cuffs. Starch helps prevent ring-around-the-collar.
Specific questions? Just ask here.