A path for what you need
Understand the rules with a small grid
Start here if you have never solved a sudoku. A nearly complete 4×4 grid lets you check the row, column and box without handling 81 cells at once.
Write possibilities without treating them as answers
Try this 9×9 example once you know the rules. Find candidates by checking all three areas and recognise when a cell has only one possible number.
Check the first move you cannot justify
If a number repeats or a cell has no candidates, use this guide to trace the error. Check the reasoning instead of wiping the whole grid.
When the grid stops moving
Keep certain numbers separate from possibilities. Look in another row, column or box before choosing at random. Not finding the next step does not prove your notes are wrong: another technique or an easier puzzle may be a better next step.
Size and difficulty are different
Moving from 4×4 to 6×6 and 9×9 can help you learn the rules with less information at first. A large grid can be easy and a small one can require care; size alone is not a useful measure of progress.
A short practice routine
Work through one area, explain each placement and check the result. If you use a hint, return to the grid and develop the deduction before opening the solution. Pencil and eraser are enough for the examples.