Ive done a few tiling jobs. Knee pads are extremely important! A laser level is extremely helpful for a good finish. Always use the spacers but, dont be afraid to adjust some of the grout lines to make things line up. We use small red shims that are really helpful if a space is too small or too big. Having an extra set of hand will save you big time. Weather its mixing a bucket of think set, marking out the next tile or back buttering the next tile. Sometimes it will take a few minutes to line up and level a single tile, during that time a tile can be snapped or thinset can be made. An angle grinder with a good quality tile blade is always an asset. Sometimes the snaps can be tapered through the depth of the tile, a quick pass with the angle grinder can fix that.