Tier 1
Adjacency elimination
The first move after every placement — a queen clears her row, her column, her colour, and all eight squares she touches.
Every other technique depends on this one being done properly. The moment a queen lands, four groups of squares die with her:
- the rest of her row
- the rest of her column
- the rest of her colour region
- the eight squares she touches, corners included
The first three are obvious. The fourth is where people lose puzzles. Queens attack diagonally in this game only at distance one — a queen on d4 does not threaten g7 — but she absolutely threatens c3, c4, c5, d3, d5, e3, e4 and e5.
Why it pays to be thorough
An empty square and a square you have not got round to crossing off look identical, and your eye treats them the same. Cross off everything immediately and the board tells you the truth: a region with one square left, a row with one square left. Leave it half done and you will stare at a solved position without seeing it.
Turn on Auto-mark blocked squares in settings and the game does this for you the instant you place a queen. Most regulars leave it on and lose nothing — the interesting work starts after this step, not during it.
The mirror image
The same fact runs backwards, and this is the part worth internalising: if a square is touched by every remaining option for some region, that square is dead before you know where the queen goes. That is locked queen placement, and it is the first technique that feels like real deduction.