How can I prevent grout from sticking in the small dimples in tiles?
If you really want to prevent any grout getting stuck in the dimples of the tile you need to mask it off. Yes- I know.. every single tile? Unfortunately, yes. 

Style and beauty is hard work.



But you can use the wide masking tapes and then just try to grout as cleanly as possible. Do not smear the grout allover the tile. Keep to the area you want to grout. Possibly apply grout with a grouting tool then smooth it with a sponge; washing it regularly.

Once its all dr peel the masking tape away. Viola.