The easiest place to start a puzzle is applying the "Rule of 45" strategy (if applicable). This rule is that all cells in a row, column or block must add to 45 (1+2+3+4+5+6+7+8+9).

Consider block 2 - there are four cages totally enclosed in this block (see green shaded cells). These cages total 39 (10 + 12 + 14 + 3). There is only one cell left in the block, therefore it must be 6 (45 - 39).

Applying the same rule of 45 logic to blocks 7 and 8, we can fill in the 7 and 5 as shown to the right. While all these examples happen to apply to blocks in this puzzle, the exact same rule would apply to rows and columns.

Now, there is another pattern we can apply the rule of 45 to.

Consider the first block. There are three cages there (shaded in green) that total 34 (14 + 9 + 11).
The remaining two cells (in yellow) must then total 11. Because that cage totals 19, the
third cell in the cage (highlighted) must then be 19 - 11, that is 8.