There are several ways of making progress. One that I use is to find a place where you are certain that one of two numbers can be used, take a guess at which it is and draw a light square round that number. From then on put a light pencil circle around each number you place until you either a) find that you have made a mistake or b) finish the puzzle. If a) then rub out those numbers with a circle round them and change the one with a square round it to its alternative and you will solve the puzzle. I hope this helps.