Rows and columns first
Each number appears once per row and column. Cross-check before you guess.
In a grid of size n, every row and every column holds each number from 1 to n exactly once. When a row already has all but one or two numbers, the gaps are easy to fill.
Look for a number that can only go in one cell of a row or column, the same "hidden single" idea as in Sudoku.
Use Notes to keep track of options. When a cell is down to one candidate, fill it in.
Practise it
The Hint button on every puzzle explains the next step in the same plain language, so you can learn as you play. Play a Futoshiki puzzle.