The numbers adjacent to your top left and bottom right should be as close to those numbers as possible.
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.
💡Create a middle diagonal (bottom-left to top-right) of tens (plus or minus-ish). That will divide the board into places for 1-10 and 10-20. A place for everything and everything in it's place.
💡Go further, create 3 middle diagonals: 5-10-15 (plus or minus-ish). Such an orderly room. Now put away all your toys.