When stopping and starting a tile job, what to do with the extra thinset from previous row's cleanup?
I used a 3" scraper - nice flexible blade which left the minimum possible.

When continuing the next day, just de-dust and fresh stuff straight on works a treat and did that for small tiles, big floor tiles and a wood parquet...

I would also put guide lines on the wall or floor to show the "glue" limits per section to be worked on...