Can't play anymore because every block I place lags the game too much but essentially all you need is, freely move on Yellow or Orange or both. Try to get as many Yellow and Orange cards that can connect into loops, get any multiplier boosts for the colors and steps. If you make a loop with even just 2 Orange/Yellow blocks and the next block is reachable within the loop, your character will move back and forth on the two Orange/Yellow blocks up to 10 times. Also recommend the one upgrade that makes Yellow equal to Orange and have Orange activate by walking by it.
My final score is 5.297683645757409e+21. Can't post it cause its too big but got a screen shot