The most starting point isn't one clue, but two. Look at the bottom edge. We have the Dark Green 3 and the Pink 2. Since they are both touching the bottom boundary, they can only have a height of 1. This forces them to be a 3x1 and a 2x1 rectangle, respectively. Together, they occupy 5 of the 6 cells on the bottom row, leaving only one cell for another shape. This is the critical first move that cracks the puzzle open.

The next undeniable clue is the Yellow 9. On a 6x6 grid, a 1x9 rectangle is impossible. Therefore, the Yellow 9 must be a 3x3 square. This is a massive anchor. Knowing the bottom row is almost entirely filled by the 3 and 2 pieces, we can deduce that the 3x3 square cannot occupy rows 4-6. Its placement is now significantly restricted to the upper-middle portion of the grid.

In the top-left, the Orange 3 is pinned in the corner. It must be either a 1x3 vertical strip or a 3x1 horizontal one. The placement of the Light Green 2 clue below it makes a 3x1 shape for the Orange piece highly probable, as it would neatly define that corner.

Once you place the 3x1 (Dark Green) and 2x1 (Pink) on the bottom row, you've established a solid foundation. This forces the placement of the shapes above them, including the Yellow 9 square. Placing the 3x3 square then creates clear boundaries for the Red, Purple, and Grey 3 pieces, leading to a cascade of logical deductions until the grid is complete.