if pentex, put them on dry...lining them up is tricky.

With the backing paper and full mask tape on the graphic, place it where you want it on the sail. Using some 1" masking tape, tape the top of the graphic to the sail with several pieces of masking tape. You've just made a hinge. Flip the graphic upside down hinging on the tape, remove the backing paper, and then carefully swing back into place and start rubbing it down from the center out. Once you've rubbed it into place, a rubber roller on a stick is very useful to fully press the graphic into the texture of the pentex.

If you are aligning a second graphic to the first with some overlap, remove the backing paper from the graphic and reapply it leaving a .25" reveal of the adhesive of the piece you are applying. The backing paper will keep the rest from sticking while you line it up with the graphic already on the sail. Carefully line up the graphic looking through the mask tape and stick the .25" you exposed. Then use THAT as the hinge, flip the graphic over, remove the backing paper, and squeegie/press into place.

Don't use application fluid when putting them on the sails. It will take 10 hours to dry before you can remove the mask tape and move onto another graphic.

Lastly, it REALLY helps to have one or two people help to hold up the ends of long graphics and keep the sail flat while you start to press them down. However, those people need to understand how to feed slack to the areas that are being pressed down while keeping the graphic taught. They can be either a huge help or a big wrinkle maker.