Mistake : Wrong bit indexing. Decide: bit or rightmost column? Stay consistent. Mistake : Forgetting to process cells in order. Column by column, row by row.
Don't jump around. Mistake : Invalid initial/final states. Start with (nothing filled). End with (everything filled). Mistake : Off-by-one in grid dimensions. Carefully index rows and columns from or . Off-by-one errors are especially common. Test on 2x2 and 2x3 grids where you can verify by hand.