On paper, mark empty cells with a small dot rather than an X: an X across a thick region border is easy to misread.
Which size to print
The 8x8 and 9x9 1-star grids fit two to a page with room for dots. Print the 10x10 2-star grid one per page: you will dot far more cells than in a 1-star grid, and the thick region borders need to stay clear. There is no colour on the sheet, so a grey-scale printer loses nothing.
Using the answer key
The answer page shows only the stars. To check a half-finished grid, compare one region at a time: a single misplaced star usually shows up as a region with no room left, and the key tells you which of its cells was the right one.