Start furthest away from the door and work backwards so you complete the part nearest the door last. You must leave the tiles for 24 hours before walking on them. If you can't do this, lay some boards down on top of the tiles and tread gently.
You can start laying from the middle of the room towards the edges but complete a whole row each time, apart from the cut tiles at the edges which can be done later. Alternatively, for a larger area, temporarily fix two guide battens at right angles, set out from the line of the first row of whole tiles.
Trowel on enough adhesive to complete a square of tiles and then use the notched edge to comb through the adhesive to make ridges with a uniform height. Place the tiles on top of the adhesive and press down. Check each tile is level and in line with the adjacent tile (4). Place a spacer next to the tile and then continue with the next one.