First look for the obvious(s). IE: Look at the three blocks on the left side. There are two #9's. One in the top block and one in the middle block. The obvious is that a 9 goes in the bottom block. Given that the #9s in the top and middle blocks are in the right and left columns within those blocks, then the 9 in the bottom block would have to go into the center column... and there is only one blank box in the bottom block's center column. So that is where the 9 goes.
When I start a SUDOKU, I look up and down the columns and then left and right. I'm looking for two of the same number within a column of blocks whether it is a vertical or horizontal column....
If you want to get good at these then you need to do them …. a lot. After a while they get much easier as you learn the tricks. IE: If a block is almost full... what numbers is it missing? Same for any row... if only one or two numbers are missing what are they and can a particular one fit in a particular block... or does that block already contain that number?
