Unlike vinyl floor tiles which meet end to end with one another, ceramic floor tile require a gap between tiles to account for expansion and contraction from the elements. When laying your ceramic floor tile, choose first what size gap you will leave.
Spacers are available to create universal size gaps across your whole floor. When initially laying out your tile patterns, use these spaces to get accurate measurements for you wall and corner cuts. When you begin you application, insert the spacers as you go in order to get the proper seal from your mortar.
After the ceramic floor tile dries in place, you can go back through your floor and remove the spacers prior to adding grout. You will find that these spacers will save you from many instances of having to redo a tile here and a tile there.