If a row, column, or region already has 8 squares filled, then the last square is easy.
You can't solve the middle column using just the middle column, but what do you see when you look elsewhere?
Try the lower-right region, looking at the regions in the same 'region row' and 'region column'. Looking at the 2's in the lower-left and upper-right, where should the 2 in the lower right go?
Good going! Now see if you can complete the whole puzzle.