Make sure that your room has a good foundation of paint and that any repairs are smooth and have been paint primed at least 48 hours before wallpapering. Assume that any “dimples” or “pimples” will show through and make appropriate repairs.
In new homes, realize that “builders” paint often does not seal the walls properly and to avoid having the wallpaper glue penetrate and damage the wallboard at time of removal, you should “size” the walls. Any new wall repairs should be properly primed or painted for the same reason. Glossy surfaces should be sanded, primed or sized to ensure grip. Easy-to-apply liquid wall size is available at your local wallpaper dealer. Often the wallpaper manufacturer’s instructions will include tips on room prep.