Lay approximately 3 feet of your largest tiles end to end. Leave room for spacers if necessary. Measure these tiles from edge to edge to determine the exact measurement. Write down the measurement.
Make a grid on the floor. Start at the corner of the longest walls and pop a chalkline across the floor. Use the measurement from Step 1 to determine where to pop new chalklines. Keep popping chalklines until you've drawn a grid on the floor.
Lay the tile on the floor, starting at the corner of the longest wall. Use a 4-foot level to ensure that your tiles are straight. Lay your bigger tiles first. Go down the grid, lining the corner of each tile up with the lines on the grid so that the bigger tiles look like steps. Repeat this process with the smaller but longer tiles so that they look like steps. The two different sets of "steps" should fit together as they go across the floor to make a step pattern.