Shade Out strategy
Shade cells so no number repeats in any row or column, shaded cells never touch, and the unshaded cells stay connected. These four patterns settle most cells, easiest first.
Beside a shaded cell
A cell beside a shaded cell must stay unshaded.
Shaded cells never touch, so no neighbour of a shaded cell can be shaded.
A copy of a cell you keep
If a cell stays unshaded, every other copy of its number in that row or column must be shaded.
Unshaded cells can't repeat a number in a line, so only one copy can stay. The one you keep decides the rest.
Pairs
When two equal numbers sit side by side, every other copy of that number in the line must be shaded.
Side by side they can't both be shaded, because shaded cells never touch, so one of them stays. Any further copy would repeat the number.
Sandwiches
A cell between two equal numbers must stay unshaded.
If it were shaded, both equal numbers would stay unshaded in the same line, and the number would repeat.