Layout flat the two surfaces you intend to join. This could be paper, fabric, foam board, whatever you are working with.
Cover both surfaces to be joined with rubber cement, apply using a brush. Covering more area than needed is o.k., the rubber cement is removable.
Allow the rubber cement to dry on both surfaces.
Join the two surfaces covered with rubber cement together. The rubber cement will stick to itself making a very tight bond.
Use the rubber cement eraser and rub any additional residue away from the unnecessary areas. The rubber cement residue will form a "build up" on the eraser. You can tear it off and throw it away.
Flood the surface with rubber cement thinner and while wet, separate the two surfaces.
Allow both surfaces to dry. This will happen quickly since the rubber cement thinner is alcohol based and evaporates.
Apply any additional rubber cement as needed. Allow it to dry. Reposition the piece.
Reposition the piece.