1. The numbers adjacent to your top left and bottom right should be as close to those numbers as possible.
2. Placing equal numbers on a (bottom-left to top-right) diagonal does not reduce your options in any meaningful way, so it should be aimed for.
3. Be Lucky.
Strategy Idea 💡: Think diagonally. The middle 3 diagonals should be 5-10-15, +/-3. This will give all tiles a place to fit.