[thomasfromcdnjs]

Haven't transplanted many trees at all, and there are probably a million factors.

A little rule I follow is;

If the plant already looks quite unhealthy, I prefer to just put it as is straight into the ground, feed it and water it. It will take longer to recover but I believe it minimises the risk of outright killing it.

If I get a very healthy plant, I will play around with it more, slice its roots, rinse it out, make a soil mix for the new roots etc

This is completely speculative but the best results I've had so far.