Selecting the right spacer depends on the tile type and desired grout line width. For standard wall tiles, 1mm to 2mm spacers are common, while floor tiles often require 3mm to 5mm to accommodate structural movement. You should choose between traditional cross-shaped spacers for standard grids, T-shaped spacers for offset or brick patterns, and long-leg spacers to prevent 'bottoming out' in deep joints. For large-format tiles, always recommend tile leveling systems (wedge and clip) to eliminate lippage and ensure a perfectly flat surface.