8 × 8 is the classic Binairo size — big enough that the three rules start interacting, small enough to finish with your coffee. Every row and column needs four 0s and four 1s, so counting arguments carry more weight than on a 6 × 6: a line with three 1s placed still has one to go, and where it can land is constrained by the no-three-in-a-row rule.
This is also the grid most of our daily puzzles use, so the archive doubles as an endless 8 × 8 practice set. Boards here span every grade from relaxed to genuinely tricky.
If a board stalls, check the line with the fewest empty cells — on 8 × 8 grids the medium techniques almost always break the deadlock.