Mastering the wisdom of wallpapering walls. What mistakes can be made and how to correct them?

Last week we corrected mistakes during the painting work. Today we are mastering the wisdom of pasting walls with wallpaper. So, what mistakes can be made in this responsible business and how to correct them?
Problem: full or partial flaking
Why
Peeling near cornices or on top of walls means that the wallpaper was pasted on a surface previously painted with glue or lime paints. Perhaps a liquid paste was used or the temperature in the room was high.
What to do
When correcting, first remove the old paint, cover the surface with glue, smear the wallpaper with a thicker paste and, as the wallpaper softens, stick it and smooth it thoroughly.
Problem: wallpaper is lagging behind architraves and skirting boards
Why
Wallpaper and places of gluing were poorly smeared with paste.
What to do
The wallpaper is folded over, twice carefully smeared with paste, the surface of the walls is also smeared with glue, and as soon as the wallpaper softens, stick it.
Problem: thick seams
Why
When pasting the new wallpaper, the seams matched the seams of the old wallpaper that had not been peeled off.
What to do
Re-glue, clean the seams.
Problem: Seam threads are visible
Why
So the edges are facing the light.
What to do
Re-paste again, starting to work from the window.
Problem: bubbles and wrinkles
Why
Bubbles and wrinkles form on wallpaper when too thick glue is applied to thin wallpaper, when the wallpaper dries too slowly, when it is carelessly smoothed, and when the wallpaper is glued before it softens from the paste.
What to do
Only plywood will help.
Problem: the wallpaper is torn in the corners of the walls
Why
Obviously, the corner of the room was covered with a solid canvas, when smeared with a paste, it stretched somewhat, and when it dried, its dimensions decreased.
What to do
Re-paste the wallpaper so that the corner of the room overlaps with the edge of the wallpaper from 1.5 to 3 centimeters.