What the numbers mean
A number counts mines in the eight surrounding squares, including diagonals. A 1 touches exactly one mine. A 2 touches exactly two. Empty revealed squares have no neighbouring mines and usually open a larger safe area.
Flag only when the count is certain
If a 1 has one hidden neighbour, that neighbour is a mine. Flag it. If a number already has the correct number of flagged neighbours, every other covered neighbour is safe. That second rule is just as important because it tells you where to click next without taking a risk.
Compare overlapping clues
Two nearby numbers often share most of their hidden neighbours. If one clue requires one more mine than the other, the extra mine must be in the square only the larger clue touches. This comparison is the bridge from basic counting to the satisfying middle game.
Do not treat flags as progress
A flag is useful when it unlocks a safe click. Placing uncertain flags can make the board harder to read and can lead to a false deduction later. It is fine to leave a square unmarked while you gather more information from another area.
When no safe move is visible
First scan the entire board again. A missed clue is common. If every remaining move is genuinely uncertain, choose the square with the best information outcome rather than clicking at random: opening a dense edge or an area connected to several clues is usually more useful than opening an isolated square.