Article: Depending upon the type of trim you have, you might be able to remove it with a hammer and screwdriver. Set the trim aside to reinstall after the slate tile is finished. Be sure to remove all the tacks and nails that stick out of the subflooring. If you have a cement floor, use a leveling compound to improve the surface. If you have a wood floor, secure loose boards so that they will not squeak.  If your wood subfloor is thinner than one and one-fourth-inch (0.6-cm), install a second layer of five-eighths-inch (1.6-cm) plywood or cement board to ensure the slate has a stable foundation. Screw these sheets into the subfloor every eight inches (20.3 cm). A cement floor can be cleaned with tri-sodium phosphate (TSP). A wooden floor can be vacuumed extensively. Paint an anti-fracture membrane onto cement subfloor. You can paint or roll it on.

What is a summary?
Remove the baseboard trim around the area you want to cover with slate tile. Remove the carpet, laminate or other flooring that is over the area. Check that your subfloor is level. Clean the floor as well as you can. Paint a coat of polyurethane on top of plywood subfloor to prevent water damage.