I always starch my fabrics before I ever cut them. I have used regular starch from the grocery store but I prefer Mary Ellen's. It is alot more expensive so I suggest that you 'hide' it from the rest of the family (in case they are ironing any of their clothes and might want to use starch).
Another word of caution...I buy my Mary Ellen's in a gallon container and then refill my little spray bottle as needed. I took a Sharpie marker and wrote on my gallon container that it is NOT to be put inside my iron. According to a quilt shop employee, someone was under the impression that one should put it in the iron (like distilled water)...that is a very big no,no. I did not want my hubby or daughters doing that so I labeled that bottle.