Make a Little Picture
Paint a picture, then check it with the same solver I used on mine. It tells you whether a player could solve it by logic alone, and if not, exactly which squares are ambiguous.
Squares outlined in yellow after a check are ones logic can't decide: the clues allow more than one picture there. Typical fixes: avoid 2×2 checkerboard patterns, avoid mirror-symmetric loose shapes, and make thin features a bit bolder.