Try thinking about what you know and dont know about a particular cell. Usually there will be at least 1 or column where there are only 3 unfilled. Think about what what 3 numbers those are. Then look at each 3X3 square, say 1 column has the number 1, 5, and 8 missing. If one 3X3 square that that column or row passes through has 1 somewhere in it, you know in that 3X3 square there cant be a 1 in the column or row you are considering. Figure out what numbers can be in a cell, then eliminate the numbers that can't be there.
The better your short term memory the more rows you can consider at once while thinking about a single empty cell.
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And as always, these are simply my worthless opinions.
My body is a channel that translates energy from the universe into happiness.
I either express information, or consume it. I am debating which to do right now.