ALL THE MATERIALS AND TOOLS LISTED ABOVE CAN BE OBTAINED IN ANY LOCAL HOME DEPOT.

PLEASE USE CAUTION WHEN CUTTING THE TILES FOR TRIM TO AVOID SERIOUS INJURY!

Proper surface

The tiles may be laid on ceiling and walls covered with lime, lime-cement, gypsum or dry plaster, chipboards, aerated concrete, construction ceramics (bricks, hollow bricks), silicates, popcorn (if it is dry and stable) etc. The surface should be even, dry, hard, stable, without any dust or grease.

Preparing the surface

Clean the surface so as to remove any dust, grease, wax or other dirt. Remove old, flaky coats of paint. Any cracks or other flaws should be filled with special fillers, gypsum or mortar.

Installing Tiles

1. Putting mastic on a tile.

On the back of a tile, put a half-inch to one-inch thick layer of mastic. (see figure 1)
The thickness of the mastic on the back of the tile should depend on a surface you are putting the tiles on. If the surface is too porous, for example popcorn ceiling, you might need to add some extra mastic. On the other hand, if the surface is flat, you may need to reduce the quantity of the mastic.
The mastic should be placed close to the corners of the tile and in the middle of it. If you feel it is necessary, add the mastic in a few more places. Some extra mastic won't bother. The mastic pieces should be a couple of inches in diameter, and they should have cone-like shapes. Don't spread the mastic so that it is completely flat.
Each piece of mastic you place on the back of a tile should look like a little hill. When you press the tile against the ceiling, the mastic will spread under the tile, making it adhere properly to the surface of the ceiling.

2. Proper gluing.

When laying tiles, you should make sure they are pressed hard enough for the mastic to adhere thoroughly to the surface without damaging the tile.

3. Parallel rows.

Lay the subsequent tiles in parallel rows.
Make sure there are no big gaps left between their edges. Move the tiles as close to each other as possible.

4. Applying caulk.

Only if needed - however should be done if installing tiles in a moist area like outside porch, shower, etc...

After all the tiles are finally glued to the ceiling, you will need to fill existing gaps between the tiles and the wall with caulk.
Use matching color or clear caulk so that it wouldn't be very obvious to a naked eye.
Since the caulk will be staying on the top of the gap, you will need to squeeze it with your finger so that it gets inside the gap.

Some of the caulk will still stay on the top of the tile after this procedure, so it needs to be removed by wiping it off with a wet sponge. Wash the sponge occasionally and squeeze out excess water so that it stays clean and wet.

Don't let the caulk stay too long on the surface of the tile because it will dry fast and so will be difficult to remove.