For appliques I take the fabric that I will use to applique onto the t-shirt and I will use a light or medium weight iron on interfacing on the back side of the fabric. Prior to applying the interfacing I iron the fabric to get rid of any wrinkles. A wrinkle in an applique will not make the finished product look neat.
In order to see the center of the shirt well I like to very lightly press a line down the exact center of the t-shirt. This helps me in the hooping process.
Turn t-shirt inside out and gently pull loose the iron on/cut away interfacing. Trim excess. Clip lose threads. Flip t-shirt again and dab off the remaining Wash n Gone with a damp sponge. Any remaining interfacing will wash away with the first washing. Sometimes I go ahead and rinse the area then toss it in the dryer for a couple of minutes to dry.
I hope you get good results with this method as well! The extra steps are well worth the time, money and effort.