More in Floors
First, get a general sense of how level the floor is. If there are any deep holes or dents, it might be necessary to prepare some quick-drying, self-leveling cement from a hardware store. Pour the cement mixture into any deep trenches and let it sit for at least 24 hours.
Once the floor is level, chip away any old mortar and then thoroughly clean the surface, probably more than once. The less dirt on the floor, the easier it is for the cement to form a strong seal between the tile and ground. Remove any trim or other fixtures around the wall at floor level. If there are any doors opening into the space, stack two tiles on top of each other to see if you will have enough clearance.
With the surface clean, lay out and diagram exactly how you want the tile to be placed. Once the tiles are in place, they can't be moved, so be sure you like the placement. Measure the dimensions of the room, and pick a spot in the center to start. Use blue chalk to mark a cross pattern into the floor. Work your way out from the center so that you can use mostly whole tiles and only have to cut the ones that will be placed along the wall edges.
Add water to the mortar until you get a peanut-butter-like consistency, preparing small batches as you go (the mixture hardens as time passes, so less is more). An easy way to do this is by attaching a paint-mixing bit to an electric drill. Use a notched floor trowel to scoop out a glob and spread it evenly across the floor using the flat side. You don't need a lot but enough to evenly coat the floor. Once the area is covered, flip the trowel and use the grooved side to spread it at a 45-degree angle.
Spread tile adhesive on the back side of the tile in a fairly thin layer. This application, along with the trenches on the floor, will ensure a permanent and strong bond between tile and ground. Gently place (do not slide) the tiles. Use spacers to maintain constant grout lines if you prefer, but it's usually fine just to eyeball it. Repeat until all whole tiles have been placed. Once you hit a wall or a space that requires a cut tile, simply measure out the dimensions and use a tile cutter to form the proper shape.
Once the floor is completely covered, mix the grout to a frozen-yogurt-type consistency, keeping in mind that small amounts go a long way. You want the grout to fall into spaces you've left between the tiles and still be easy to spread. Dump out some grout, then use a grout float to spread it around, making sure there aren't any gaps or bubbles. Scrape off any excess by wiping diagonally across the tiles. Follow the scraping with a wet sponge, having a bucket filled with water on hand to wash out the excess. It will take a few passes with a sponge to remove the entire residue from the tile surfaces. Let tiles stand for 24 hours.