How do you get Wonder Under or Steam a Seam to stick?

There has to be a secret or something I'm doing wrong. I cannot get a fusible to stick. I've tried a couple different products, prewashed my fabrics without fabric softener, no dryer sheets and the edges or sometimes the whole piece lifts off after it cools. Could it be our city water? I do believe we have hard water here. I would love it if someone could post some tips on how to use fusibles properly, how to prepare fabric for use, and maybe tell me what the bleep I'm doing wrong:)