I use either Niagra in the non-aerosol bottle or Mary Ellen's Best Press. My favorite is Best Press but it is pricy. I always ask for it on my Christmas list.
To successfully starch you need to let the liquid soak into the fabric. Best Press is designed to do this quickly and doesn't leave residue on my iron like spray starch does. You will minimize or eliminate flaking if you let the starch soak in. I usually put my fabric in a plastic bag and spray the starch on the fabric. I then close the bag and kneed it to distribute the starch and then let it sit for a while for the starch to penetrate the fabric. The plastic bag keeps it from drying out much like in days past people put sprinkled clothes in plastic bags for ironing.
To clean residue off my iron I use a magic eraser (like Mr. Clean one). I have a shiny sole plate on my iron. I don't know if it would work with a teflon coated sole plate. A wet eraser on a cold iron works great and much cheaper than the iron cleaners you can buy.