Use notes only where the grid needs them
Start with rows, columns and boxes that have relatively few empty cells. For each empty cell, note only the digits that are absent from all three units.
Do not treat a candidate as a guess. It means only that the digit has not yet been ruled out. Place a full-size answer only when one candidate remains in a cell, or when a digit has only one possible position in a row, column or box.
Update immediately after every placement
A correct placement changes three areas at once: its row, its column and its 3×3 box. Remove that digit from every affected candidate list before looking for the next move.
This small update step prevents stale notes. It can also reveal a new single straight away, which is safer and faster than starting a fresh scan of the whole grid.
Look for pairs before adding more ink
If the same two candidates occupy exactly two cells in one row, column or box, those digits must fill those cells in some order. They can be removed from other candidate lists in that unit.
Keep the conclusion local: a pair in a row affects that row, while a pair in a box affects that box. Avoid removing candidates elsewhere unless the same cells also form the pattern in the intersecting unit.
Reset the notes when they stop helping
Messy notes are a signal to pause. Recheck one unit at a time, erase candidates contradicted by placed digits and confirm that every remaining mark is still possible.
Fun IQ’s Daily Sudoku lets you practise the routine without timing pressure. Use Check progress after a short sequence of logical placements, not after every cell, so the puzzle still rewards your own deductions.