You should not tile over wallpaper glossy surfaces lead paint or plywood.
Tiling onto plasterboard youtube.
If you re not sure if you have lead paint test kits are available.
As for setting out centre your walls and walk tiles into corners to see what size of cuts you will have.
Tiling onto plasterboard walls.
However tiling over tile can add quite a bit of thickness so make sure your wall can handle the weight.
It should be a minimum 12 5mm thick when fixed to timber framing or battening and fixed in accordance with the manufacturers recommendations.
Dont use pva as the other guys have stated.
Tile onto p b dont skimm it bring weight issues into tile fixing.
Learn how to tile a bathroom with an instructional video from bunnings w.
Any windows tile from centre of these.
As its a nice flat surface spread the adhesive onto the wall with a notched trowel then just apply the tiles with firm but steady pressure and use spacers i normally get a 2x1 batten and tack it to the wall 1 tile and 2 spacing a high from the work top then tile from that upwards when dry remove the batten and tile down to the worktop then grout but leave the last tile space to allow sealant in.
Let us know ansewers to the above 2 questions.
You may tile over existing tile painted or unpainted drywall plaster and textured walls.