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One very helpful strategy for me is to use the the numbers in the top right corner. This helps me know which numbers are possible in each square so that I don't have to choose from as many options and the answer becomes clearer to me.

e.g. If multiplied together two numbers have to equal 4, I know that it has to be a 4 and a 1. This is because I can't do 2x2 or something like that. I will also often find that the one has to go there because all the other squares that are in a row don't have a one which means that number needs to be a 4. This tells me that the other number is a one.