If the humidity is high I heat the lams with a hair dryer . I use thin enough lams that a few minutes removes any excess moisture. Most times I do not preheat. Thelams are cool when you apply the glue anyway so actually helping with adhesion is a mute point in my opinion. What you do not want is gas bubbles under the glass which look ugly and cause delaminations if to much. Always preheat if doing extremely dark laminations under clear glass. Walnut, Cocabola ect.