From: United States
One pattern to look for is for pairs of numbers that are adjacent orthogonally and diagonally.
See that 3/4 in the bottom right? And the 5/3/4 in the bottom left? You can circle the (uncircled) five - if it were blacked out, you'd have to black out the three and the four in the bottom right, and you can't black them both out.
Another pattern to look for is the single circle surrounded by pairs of numbers - such as the 8/4/8 or the 8/7/8 at the bottom. No matter which one is circled, it effectively creates a wall where the middle number is. (If I was solving this on paper, I'd draw a line connecting the blacked-out 4 and 2 (for the 8/4/8), and the blacked-out 4 and the wall (through the 7 of the 8/7/8). No matter which of the eights are blacked out, you'll need to have the three circled to connect the one with the rest of the circles.