hi mate
use what dave says, nothing else..
1, cut all you boards first ready to fix
2. mix you addy in a bucket, it must be thick enough to hang on to your trowel when turned upside down.
3. dab on the wall every 12 in as you say, so if its a 8x4 board you want 5 along the top and 9 up the side and in corresponding lines vertically.
4. use a trowel or the rear of a bucket trowel to slap the dabs on, they need to be around 25mm thick minand the boards will press in about 12.5mm allowing for any cables to go down the back etc.
5. tap the board with a 6ft straight edge/level at either side, then when you have fixed 2 boards side by side, put your straight edge across the boards horizontally, to ensure they dont dip in , in the middle. do this till you reach the end of the wall. you can put a square in the corners aswell to make sure everything is spot on
6. keep the boards off the floor by place 2 off cuts of plaster boards under the 8x4 or 6x3 boards (stops water penetration/damp)
7. finally, ensure there is a full dab of adhesive around all sockets and switches to ensure pressure testing.
8, finally finally...if the walls are really old and dusty, brush down and wet, or even seal with water and pva at around 4to1 ratio.
if its newish block/brick work , then just get em up
hope this helps
ed