Use the Overlap Technique

Place a block mentally as far left as possible and then as far right as possible. Any cells covered in both positions must be filled.

Consider a ten-cell line with the clue 8.

Leftmost position:

■ ■ ■ ■ ■ ■ ■ ■ · ·

Rightmost position:

· · ■ ■ ■ ■ ■ ■ ■ ■

The six central cells overlap:

· · ■ ■ ■ ■ ■ ■ · ·

Those six cells must be filled regardless of the final position of the block.

For one block, the number of guaranteed overlapping cells can be calculated as:

Guaranteed cells = 2 × block length − line length

For a block of 8 in a line of 10:

2 × 8 − 10 = 6

Therefore, six cells can be filled immediately.