Always read the flooring manufacturers recommendations and instructions before installing the underlayment.
Before rolling out the underlayment, be sure to sweep, vacuum, and remove all debris on the substructure.
Fill in any significant holes, gaps or breaks that may exist on the substructure.
Roll out the Underlayment over the substructure surface.
Overlap seams by 6" with a 3mm film tape, duct tape, or similar pressure-sensitive tape that meets/exceeds the water vapor transmission ratings suggested by the flooring manufacturer.