For unpasted wallpaper products, place the strip pattern side down on a large table or on the floor if thats where you choose to work.
With a paint roller or wide  brush, lightly and gently, coat the back of the strip with the paste recommended by the manufacturer.

Prepasted Products: Watertrays, No doubt the WORST tool that has ever hit the market. Most wallcoverings are designed to have some soak time. Because of the design of these trays it is Impossible to get a even amount of soak time over the entire sheet of wallcovering, its rolled up into a tube!
This can lead to part of the sheet expanding more then another part. Making it extremely difficult to hang. Not only that but with each piece of wallpaper soaking in the tray,more and more paste is left in the water and by the second or third sheet your are soaking the face of the paper with paste meaning you have to wash the entire sheet.
Why go thru the grief, use the trays as a flower box.

Buy yourself a pad painter or use a roller with a short nap 3/8" roller cover. Lay the wallcovering out on a table or counter and wet it with the pad painter or roller that you have dipped in water. This also allows the use of prepasted activators.

Fold and book the wallcovering by folding the top half towards the middle,about 1/3rd of the length of the sheet, paste to paste, and the bottom up to the edge of the first fold. Fold pasted side to pasted side, keeping the edges aligned.

Allow the wallcovering time to expand on the table and it won't try to expand on the wall.

OK, Lets Hang it!

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